Pyrrolobenzodiazepines

ABSTRACT

A compound with the formula I: wherein: R 2  is of formula II: where A is a C 5-7  aryl group, X is selected from the group comprising: NHNH 2 , CONHNH 2 , formula III, formula IV, and either: (i) Q 1  is a single bond, and Q 2  is selected from a single bond and —Z—(CH 2 ) n —, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q 1  is —CH═CH—, and Q 2  is a single bond; R 12  is a C 5-10  aryl group, optionally substituted by one or more substituents selected from the group comprising: halo, nitro, cyano, ether, C 1-7  alkyl, C 3-7  heterocyclyl and bis-oxy-C 1-3  alkylene; R 6  and R 9  are independently selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NRR′, nitro, Me 3 Sn and halo; where R and R′ are independently selected from optionally substituted C 1-12  alkyl, C 3-20  heterocyclyl and C 5-20  aryl groups; R 7  is selected from H, R, OH, OR, SH, SR, NH 2 , NHR, NHRR′, nitro, Me 3 Sn and halo; either: (a) R 10  is H, and R 11  is OH, OR A , where R A  is C 1-4  alkyl; (b) R 10  and R 11  form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R 10  is H and R 11  is SO z M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R″ is a C 3-12  alkylene group, which chain may be interrupted by one or more heteroatoms, and/or aromatic rings; Y and Y′ are selected from O, S, or NH; R 6′ , R 7′ , R 9′  are selected from the same groups as R 6 , R 7  and R 9  respectively and R 10′  and R 11′  are the same as R 10  and R 11 , wherein if R 11  and R 11′  are SO z M, M may represent a divalent pharmaceutically acceptable cation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 of International Application No. PCT/EP2012/070231 filed Oct. 12, 2012, and claims the benefit of U.S. Provisional Application No. 61/547,204 filed Oct. 14, 2011, which is incorporated by reference herein.

The present invention relates to pyrrolobenzodiazepines (PBDs), in particular pyrrolobenzodiazepine dimers having a C2-C3 double bond and an aryl group at the C2 position in each monomer unit, and their inclusion in targeted conjugates.

BACKGROUND TO THE INVENTION

Some pyrrolobenzodiazepines (PBDs) have the ability to recognise and bond to specific sequences of DNA; the preferred sequence is PuGPu. The first PBD antitumour antibiotic, anthramycin, was discovered in 1965 (Leimgruber, et al., J. Am. Chem. Soc., 87, 5793-5795 (1965); Leimgruber, et al., J. Am. Chem. Soc., 87, 5791-5793 (1965)). Since then, a number of naturally occurring PBDs have been reported, and numerous synthetic routes have been developed to a variety of analogues (Thurston, et al., Chem. Rev. 1994, 433-465 (1994); Antonow, D. and Thurston, D. E., Chem. Rev. 2011 111 (4), 2815-2864). Family members include abbeymycin (Hochlowski, et al., J. Antibiotics, 40, 145-148 (1987)), chicamycin (Konishi, et al., J. Antibiotics, 37, 200-206 (1984)), DC-81 (Japanese Patent 58-180 487; Thurston, et al., Chem. Brit., 26, 767-772 (1990); Bose, et al., Tetrahedron, 48, 751-758 (1992)), mazethramycin (Kuminoto, et al., J. Antibiotics, 33, 665-667 (1980)), neothramycins A and B (Takeuchi, et al., J. Antibiotics, 29, 93-96 (1976)), porothramycin (Tsunakawa, et al., J. Antibiotics, 41, 1366-1373 (1988)), prothracarcin (Shimizu, et al, J. Antibiotics, 29, 2492-2503 (1982); Langley and Thurston, J. Org. Chem., 52, 91-97 (1987)), sibanomicin (DC-102)(Hara, et al., J. Antibiotics, 41, 702-704 (1988); Itoh, et al., J. Antibiotics, 41, 1281-1284 (1988)), sibiromycin (Leber, et al., J. Am. Chem. Soc., 110, 2992-2993 (1988)) and tomamycin (Arima, et al., J. Antibiotics, 25, 437-444 (1972)). PBDs are of the general structure:

They differ in the number, type and position of substituents, in both their aromatic A rings and pyrrolo C rings, and in the degree of saturation of the C ring. In the B-ring there is either an imine (N═C), a carbinolamine (NH—CH(OH)), or a carbinolamine methyl ether (NH—CH(OMe)) at the N10-C11 position which is the electrophilic centre responsible for alkylating DNA. All of the known natural products have an (S)-configuration at the chiral C11a position which provides them with a right-handed twist when viewed from the C ring towards the A ring. This gives them the appropriate three-dimensional shape for isohelicity with the minor groove of B-form DNA, leading to a snug fit at the binding site (Kohn, In Antibiotics III. Springer-Verlag, New York, pp. 3-11 (1975); Hurley and Needham-VanDevanter, Acc. Chem. Res., 19, 230-237 (1986)). Their ability to form an adduct in the minor groove, enables them to interfere with DNA processing, hence their use as antitumour agents.

It has been previously disclosed that the biological activity of these molecules can be potentiated by joining two PBD units together through their C8/C′-hydroxyl functionalities via a flexible alkylene linker (Bose, D. S., et al., J. Am. Chem. Soc., 114, 4939-4941 (1992); Thurston, D. E., et al., J. Org. Chem., 61, 8141-8147 (1996)). The PBD dimers are thought to form sequence-selective DNA lesions such as the palindromic 5′-Pu-GATC-Py-3′ interstrand cross-link (Smellie, M., et al., Biochemistry, 42, 8232-8239 (2003); Martin, C., et al., Biochemistry, 44, 4135-4147) which is thought to be mainly responsible for their biological activity. One example of a PBD dimmer, SG2000 (SJG-136):

has recently entered Phase II clinical trials in the oncology area (Gregson, S., et al., J. Med. Chem., 44, 737-748 (2001); Alley, M. C., et al., Cancer Research, 64, 6700-6706 (2004); Hartley, J. A., et al., Cancer Research, 64, 6693-6699 (2004)).

More recently, the present inventors have previously disclosed in WO 2005/085251, dimeric PBD compounds bearing C2 aryl substituents, such as SG2202 (ZC-207):

and in WO2006/111759, bisulphites of such PBD compounds, for example SG2285 (ZC-423):

These compounds have been shown to be highly useful cytotoxic agents (Howard, P. W., et al., Bioorg. Med. Chem. (2009), 19 (22), 6463-6466, doi: 10.1016/j.bmc1.2009.09.012).

Due to the manner in which these highly potent compounds act in cross-linking DNA, these molecules have been made symmetrically. This provides for straightforward synthesis, either by constructing the PBD moieties simultaneously having already formed the dimer linkage, or by reacting already constructed PBD moieties with the dimer linking group.

WO 2010/043880 discloses unsymmetrical dimeric PBD compound bearing aryl groups in the C2 position of each monomer, where one of these aryl groups bears a substituent designed to provide an anchor for linking the compound to another moiety. Co-pending International application PCT/US2011/032664, filed 15 Apr. 2011, published as WO 2011/130613, discloses the inclusion of these PBD dimer compounds in targeted conjugates. Co-pending International application PCT/US2011/032668, filed 15 Apr. 2011, published as WO 2011/130616, discloses unsymmetrical dimeric PBD compound bearing an aryl group in the C2 position of one monomer bearing a substituent designed to provide an anchor for linking the compound to another moiety, the other monomer bearing a non-aromatic group in the C2 position. The inclusion of these compounds in targeted conjugates is also disclosed.

DISCLOSURE OF THE INVENTION

The present inventors have developed further unsymmetrical dimeric PBD compounds for inclusion in targeted conjugates, where the dimer has aryl groups in the C2 position of each monomer, where one of these groups bears particular substituents designed to provide an anchor for linking the compound to another moiety. These particular substituent groups may offer advantages in the preparation and use of the compounds, particularly in their biological properties and the synthesis of conjugates, and the biological properties of these conjugates

The present invention comprises a compound with the formula I:

wherein: R² is of formula II:

where A is a C₅₋₇ aryl group, X is selected from the group comprising: NHNH₂, CONHNH₂,

and either: (i) Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is a C₅₋₁₀ aryl group, optionally substituted by one or more substituents selected from the group comprising: halo, nitro, cyano, ether, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are independently selected from H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; where R and R′ are independently selected from optionally substituted C₁₋₁₂ alkyl, C₃₋₂₀ heterocyclyl and C₅₋₂₀ aryl groups; R⁷ is selected from H, R, OH, OR, SH, SR, NH₂, NHR, NHRR′, nitro, Me₃Sn and halo; either: (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), where R^(A) is C₁₋₄ alkyl; or (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R¹⁰ is H and R¹¹ is SO_(z)M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more heteroatoms, e.g. O, S, NR^(N2) (where R^(N2) is H or C₁₋₄ alkyl), and/or aromatic rings, e.g. benzene or pyridine; Y and Y′ are selected from O, S, or NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation.

A second aspect of the present invention provides the use of a compound of the first aspect of the invention in the manufacture of a medicament for treating a proliferative disease. The second aspect also provides a compound of the first aspect of the invention for use in the treatment of a proliferative disease.

One of ordinary skill in the art is readily able to determine whether or not a candidate conjugate treats a proliferative condition for any particular cell type. For example, assays which may conveniently be used to assess the activity offered by a particular compound are described in the examples below.

A third aspect of the present invention comprises a compound of formula II:

wherein: R² is of formula II:

where A is a C₅₋₇ aryl group, X is selected from the group comprising: NHNH₂, CONHNH₂,

and either: (i) Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is a C₅₋₁₀ aryl group, optionally substituted by one or more substituents selected from the group comprising: halo, nitro, cyano, ether, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are independently selected from H, R, OH, OR, SH, SR, NH₂, NHR, NRR′, nitro, Me₃Sn and halo; where R and R′ are independently selected from optionally substituted C₁₋₁₂ alkyl, C₃₋₂₀ heterocyclyl and C₅₋₂₀ aryl groups; R⁷ is selected from H, R, OH, OR, SH, SR, NH₂, NHR, NHRR′, nitro, Me₃Sn and halo; either: (a) R¹⁰ is carbamate nitrogen protecting group, and R¹¹ is O-Prot^(O), wherein Prot^(O) is an oxygen protecting group; or (b) R¹⁰ is a hemi-aminal nitrogen protecting group and R¹¹ is an oxo group; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more heteroatoms, e.g. O, S, NR^(N2) (where R^(N2) is H or C₁₋₄ alkyl), and/or aromatic rings, e.g. benzene or pyridine; Y and Y′ are selected from O, S, or NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹.

A fourth aspect of the present invention comprises a method of making a compound of formula I from a compound of formula II by deprotection of the imine bond.

The unsymmetrical dimeric PBD compounds of the present invention are made by different strategies to those previously employed in making symmetrical dimeric PBD compounds. In particular, the present inventors have developed a method which involves adding each each C2 substituent to a symmetrical PBD dimer core in separate method steps. Accordingly, a fifth aspect of the present invention provides a method of making a compound of the first or third aspect of the invention, comprising at least one of the method steps set out below.

In a sixth aspect, the present invention relates to Conjugates comprising dimers of PBDs linked to a targeting agent, wherein the PBD idimer is of formula I (supra).

In some embodiments, the Conjugates have the following formula III: L-(LU-D)_(p)  (III) wherein L is a Ligand unit (i.e., a targeting agent), LU is a Linker unit and D is a Drug unit that is a PBD dimer (see below). The subscript p is an integer of from 1 to 20. Accordingly, the Conjugates comprise a Ligand unit covalently linked to at least one Drug unit by a Linker unit. The Ligand unit, described more fully below, is a targeting agent that binds to a target moiety. The Ligand unit can, for example, specifically bind to a cell component (a Cell Binding Agent) or to other target molecules of interest. Accordingly, the present invention also provides methods for the treatment of, for example, various cancers and autoimmune disease. These methods encompass the use of the Conjugates wherein the Ligand unit is a targeting agent that specifically binds to a target molecule. The Ligand unit can be, for example, a protein, polypeptide or peptide, such as an antibody, an antigen-binding fragment of an antibody, or other binding agent, such as an Fc fusion protein.

The PBD dimer D is of formula I, except that X is selected from the group comprising: *NHNH^(q), *CONHNH^(q),

where * indicates where the group is bound to the PBD moiety, and q indicates where the group is bound to the Linker Unit.

The drug loading is represented by p, the number of drug molecules per Ligand unit (e.g., an antibody). Drug loading may range from 1 to 20 Drug units (D) per Ligand unit (e.g., Ab or mAb). For compositions, p represents the average drug loading of the Conjugates in the composition, and p ranges from 1 to 20.

In some embodiments, p is from about 1 to about 8 Drug units per Ligand unit. In some embodiments, p is 1. In some embodiments, p is 2. In some embodiments, p is from about 2 to about 8 Drug units per Ligand unit. In some embodiments, p is from about 2 to about 6, 2 to about 5, or 2 to about 4 Drug units per Ligand unit. In some embodiments, p is about 2, about 4, about 6 or about 8 Drug units per Ligand unit.

The average number of Drugs units per Ligand unit in a preparation from a conjugation reaction may be characterized by conventional means such as mass spectroscopy, ELISA assay, and HPLC. The quantitative distribution of Conjugates in terms of p may also be determined. In some instances, separation, purification, and characterization of homogeneous Conjugates, where p is a certain value, from Conjugates with other drug loadings may be achieved by means such as reverse phase HPLC or electrophoresis.

In a seventh aspect, the present invention relates to Linker-Drug compounds (i.e., Drug-Linkers) comprising dimers of PBDs linked to a linking unit. These Drug-linkers can be used as intermediates for the synthesis of Conjugates comprising dimers of PBDs linked to a targeting agent.

These Drug-Linkers have the following formula V: LU-D  (V) or a pharmaceutically acceptable salt or solvate thereof, wherein LU is a Linker unit and D is a Drug unit that is a PBD dimer.

In the Drug-Linkers of the present invention, the PBD dimer D is of formula I, or a pharmaceutically acceptable salt or solvate thereof, except that X is selected from the group comprising: *NHNH^(q), *CONHNH^(q),

where * indicates where the group is bound to the PBD moiety, and q indicates where the group is bound to the Linker Unit.

DEFINITIONS

Pharmaceutically Acceptable Cations Examples of pharmaceutically acceptable monovalent and divalent cations are discussed in Berge, et al., J. Pharm. Sci., 66, 1-19 (1977), which is incorporated herein by reference.

The pharmaceutically acceptable cation may be inorganic or organic.

Examples of pharmaceutically acceptable monovalent inorganic cations include, but are not limited to, alkali metal ions such as Na⁺ and K⁺. Examples of pharmaceutically acceptable divalent inorganic cations include, but are not limited to, alkaline earth cations such as Ca²⁺ and Mg²⁺. Examples of pharmaceutically acceptable organic cations include, but are not limited to, ammonium ion (i.e. NH₄ ⁺) and substituted ammonium ions (e.g. NH₃R⁺, NH₂R₂ ⁺, NHR₃ ⁺, NR₄ ⁺). Examples of some suitable substituted ammonium ions are those derived from: ethylamine, diethylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH₃)₄ ⁺.

Substituents

The phrase “optionally substituted” as used herein, pertains to a parent group which may be unsubstituted or which may be substituted.

Unless otherwise specified, the term “substituted” as used herein, pertains to a parent group which bears one or more substituents. The term “substituent” is used herein in the conventional sense and refers to a chemical moiety which is covalently attached to, or if appropriate, fused to, a parent group. A wide variety of substituents are well known, and methods for their formation and introduction into a variety of parent groups are also well known.

Examples of substituents are described in more detail below.

C₁₋₁₂ alkyl: The term “C₁₋₁₂ alkyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a carbon atom of a hydrocarbon compound having from 1 to 12 carbon atoms, which may be aliphatic or alicyclic, and which may be saturated or unsaturated (e.g. partially unsaturated, fully unsaturated). Thus, the term “alkyl” includes the sub-classes alkenyl, alkynyl, cycloalkyl, etc., discussed below.

Examples of saturated alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), propyl (C₃), butyl (C₄), pentyl (C₅), hexyl (C₆) and heptyl (C₇).

Examples of saturated linear alkyl groups include, but are not limited to, methyl (C₁), ethyl (C₂), n-propyl (C₃), n-butyl (C₄), n-pentyl (amyl) (C₅), n-hexyl (C₆) and n-heptyl (C₇).

Examples of saturated branched alkyl groups include iso-propyl (C₃), iso-butyl (C₄), sec-butyl (C₄), tert-butyl (C₄), iso-pentyl (C₅), and neo-pentyl (C₅).

C₂₋₁₂ Alkenyl: The term “C₂₋₁₂ alkenyl” as used herein, pertains to an alkyl group having one or more carbon-carbon double bonds.

Examples of unsaturated alkenyl groups include, but are not limited to, ethenyl (vinyl, —CH═CH₂), 1-propenyl (—CH═CH—CH₃), 2-propenyl (allyl, —CH—CH═CH₂), isopropenyl (1-methylvinyl, —C(CH₃)═CH₂), butenyl (C₄), pentenyl (C₅), and hexenyl (C₆).

C₂₋₁₂ alkynyl: The term “C₂₋₁₂ alkynyl” as used herein, pertains to an alkyl group having one or more carbon-carbon triple bonds.

Examples of unsaturated alkynyl groups include, but are not limited to, ethynyl (—C≡CH) and 2-propynyl (propargyl, —CH₂—C≡CH).

C₃₋₁₂ cycloalkyl: The term “C₃₋₁₂ cycloalkyl” as used herein, pertains to an alkyl group which is also a cyclyl group; that is, a monovalent moiety obtained by removing a hydrogen atom from an alicyclic ring atom of a cyclic hydrocarbon (carbocyclic) compound, which moiety has from 3 to 7 carbon atoms, including from 3 to 7 ring atoms.

Examples of cycloalkyl groups include, but are not limited to, those derived from:

-   -   saturated monocyclic hydrocarbon compounds:         cyclopropane (C₃), cyclobutane (C₄), cyclopentane (C₅),         cyclohexane (C₆), cycloheptane (C₇), methylcyclopropane (C₄),         dimethylcyclopropane (C₅), methylcyclobutane (C₅),         dimethylcyclobutane (C₆), methylcyclopentane (C₆),         dimethylcyclopentane (C₇) and methylcyclohexane (C₇);     -   unsaturated monocyclic hydrocarbon compounds:         cyclopropene (C₃), cyclobutene (C₄), cyclopentene (C₅),         cyclohexene (C₆), methylcyclopropene (C₄), dimethylcyclopropene         (C₅), methylcyclobutene (C₅), dimethylcyclobutene (C₆),         methylcyclopentene (C₆), dimethylcyclopentene (C₇) and         methylcyclohexene (C₇); and     -   saturated polycyclic hydrocarbon compounds:         norcarane (C₇), norpinane (C₇), norbornane (C₇).

C₃₋₂₀ heterocyclyl: The term “C₃₋₂₀ heterocyclyl” as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from a ring atom of a heterocyclic compound, which moiety has from 3 to 20 ring atoms, of which from 1 to 10 are ring heteroatoms. Preferably, each ring has from 3 to 7 ring atoms, of which from 1 to 4 are ring heteroatoms.

In this context, the prefixes (e.g. C₃₋₂₀, C₃₋₇, C₅₋₆, etc.) denote the number of ring atoms, or range of number of ring atoms, whether carbon atoms or heteroatoms. For example, the term “C₅₋₆heterocyclyl”, as used herein, pertains to a heterocyclyl group having 5 or 6 ring atoms.

Examples of monocyclic heterocyclyl groups include, but are not limited to, those derived from:

N₁: aziridine (C₃), azetidine (C₄), pyrrolidine (tetrahydropyrrole) (C₅), pyrroline (e.g., 3-pyrroline, 2,5-dihydropyrrole) (C₅), 2H-pyrrole or 3H-pyrrole (isopyrrole, isoazole) (C₅), piperidine (C₆), dihydropyridine (C₆), tetrahydropyridine (C₆), azepine (C₇); O₁: oxirane (C₃), oxetane (C₄), oxolane (tetrahydrofuran) (C₅), oxole (dihydrofuran) (C₅), oxane (tetrahydropyran) (C₆), dihydropyran (C₆), pyran (C₆), oxepin (C₇); S₁: thiirane (C₃), thietane (C₄), thiolane (tetrahydrothiophene) (C₅), thiane (tetrahydrothiopyran) (C₆), thiepane (C₇); O₂: dioxolane (C₅), dioxane (C₆), and dioxepane (C₇); O₃: trioxane (C₆); N₂: imidazolidine (C₅), pyrazolidine (diazolidine) (C₅), imidazoline (C₅), pyrazoline (dihydropyrazole) (C₅), piperazine (C₆); N₁O₁: tetrahydrooxazole (C₅), dihydrooxazole (C₅), tetrahydroisoxazole (C₅), dihydroisoxazole (C₅), morpholine (C₆), tetrahydrooxazine (C₆), dihydrooxazine (C₆), oxazine (C₆); N₁S₁: thiazoline (C₅), thiazolidine (C₅), thiomorpholine (C₆); N₂O₁: oxadiazine (C₆); O₁S₁: oxathiole (C₅) and oxathiane (thioxane) (C₆); and, N₁O₁S₁: oxathiazine (C₆).

Examples of substituted monocyclic heterocyclyl groups include those derived from saccharides, in cyclic form, for example, furanoses (C₅), such as arabinofuranose, lyxofuranose, ribofuranose, and xylofuranse, and pyranoses (C₆), such as allopyranose, altropyranose, glucopyranose, mannopyranose, gulopyranose, idopyranose, galactopyranose, and talopyranose.

C₅₋₂₀ aryl: The term “C₅₋₂₀ aryl”, as used herein, pertains to a monovalent moiety obtained by removing a hydrogen atom from an aromatic ring atom of an aromatic compound, which moiety has from 3 to 20 ring atoms. Preferably, each ring has from 5 to 7 ring atoms.

In this context, the prefixes (e.g. C₃₋₂₀, C₅₋₇, C₅₋₆, etc.) denote the number of ring atoms, or range of number of ring atoms, whether carbon atoms or heteroatoms. For example, the term “C₅₋₆ aryl” as used herein, pertains to an aryl group having 5 or 6 ring atoms.

The ring atoms may be all carbon atoms, as in “carboaryl groups”.

Examples of carboaryl groups include, but are not limited to, those derived from benzene (i.e. phenyl) (CO, naphthalene (C₁₀), azulene (C₁₀), anthracene (C₁₄), phenanthrene (C₁₄), naphthacene (C₁₀), and pyrene (C₁₆).

Examples of aryl groups which comprise fused rings, at least one of which is an aromatic ring, include, but are not limited to, groups derived from indane (e.g. 2,3-dihydro-1H-indene) (C₉), indene (C₉), isoindene (C₉), tetraline (1,2,3,4-tetrahydronaphthalene (C₁₀), acenaphthene (C₁₂), fluorene (C₁₃), phenalene (C₁₃), acephenanthrene (C₁₅), and aceanthrene (C₁₆).

Alternatively, the ring atoms may include one or more heteroatoms, as in “heteroaryl groups”. Examples of monocyclic heteroaryl groups include, but are not limited to, those derived from:

N₁: pyrrole (azole) (C₅), pyridine (azine) (C₆);

O₁: furan (oxole) (C₅);

S₁: thiophene (thiole) (C₅);

N₁O₁: oxazole (C₅), isoxazole (C₅), isoxazine (C₆);

N₂O₁: oxadiazole (furazan) (C₅);

N₃O₁: oxatriazole (C₅);

N₁S₁: thiazole (C₅), isothiazole (C₅);

N₂: imidazole (1,3-diazole) (C₅), pyrazole (1,2-diazole) (C₅), pyridazine (1,2-diazine) (C₆), pyrimidine (1,3-diazine) (C₆) (e.g., cytosine, thymine, uracil), pyrazine (1,4-diazine) (C₆);

N₃: triazole (C₅), triazine (C₆); and,

N₄: tetrazole (C₅).

Examples of heteroaryl which comprise fused rings, include, but are not limited to:

-   -   C₉ (with 2 fused rings) derived from benzofuran (O₁),         isobenzofuran (O₁), indole (N₁), isoindole (N₁), indolizine         (N₁), indoline (N₁), isoindoline (N₁), purine (N₄) (e.g.,         adenine, guanine), benzimidazole (N₂), indazole (N₂),         benzoxazole (N₁O₁), benzisoxazole (N₁O₁), benzodioxole (O₂),         benzofurazan (N₂O₁), benzotriazole (N₃), benzothiofuran (S₁),         benzothiazole (N₁S₁), benzothiadiazole (N₂S);     -   C₁₀ (with 2 fused rings) derived from chromene (O₁), isochromene         (O₁), chroman (O₁), isochroman (O₁), benzodioxan (O₂), quinoline         (N₁), isoquinoline (N₁), quinolizine (N₁), benzoxazine (N₁O₁),         benzodiazine (N₂), pyridopyridine (N₂), quinoxaline (N₂),         quinazoline (N₂), cinnoline (N₂), phthalazine (N₂),         naphthyridine (N₂), pteridine (N₄);     -   C₁₁ (with 2 fused rings) derived from benzodiazepine (N₂);     -   C₁₃ (with 3 fused rings) derived from carbazole (N₁),         dibenzofuran (O₁), dibenzothiophene (S₁), carboline (N₂),         perimidine (N₂), pyridoindole (N₂); and,

C₁₄ (with 3 fused rings) derived from acridine (N₁), xanthene (O₁), thioxanthene (S₁), oxanthrene (O₂), phenoxathiin (O₁S₁), phenazine (N₂), phenoxazine (N₁O₁), phenothiazine (N₁S₁), thianthrene (S₂), phenanthridine (N₁), phenanthroline (N₂), phenazine (N₂).

The above groups, whether alone or part of another substituent, may themselves optionally be substituted with one or more groups selected from themselves and the additional substituents listed below.

Halo: —F, —Cl, —Br, and —I.

Hydroxy: —OH.

Ether: —OR, wherein R is an ether substituent, for example, a C₁₋₇ alkyl group (also referred to as a C₁₋₇ alkoxy group, discussed below), a C₃₋₂₀ heterocyclyl group (also referred to as a C₃₋₂₀ heterocyclyloxy group), or a C₅₋₂₀ aryl group (also referred to as a C₅₋₂₀ aryloxy group), preferably a C₁₋₇alkyl group. Alkoxy: —OR, wherein R is an alkyl group, for example, a C₁₋₇ alkyl group. Examples of C₁₋₇ alkoxy groups include, but are not limited to, —OMe (methoxy), —OEt (ethoxy), —O(nPr) (n-propoxy), —O(iPr) (isopropoxy), —O(nBu) (n-butoxy), —O(sBu) (sec-butoxy), —O(iBu) (isobutoxy), and —O(tBu) (tert-butoxy). Acetal: —CH(OR¹)(OR²), wherein R¹ and R² are independently acetal substituents, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group, or, in the case of a “cyclic” acetal group, R¹ and R², taken together with the two oxygen atoms to which they are attached, and the carbon atoms to which they are attached, form a heterocyclic ring having from 4 to 8 ring atoms. Examples of acetal groups include, but are not limited to, —CH(OMe)₂, —CH(OEt)₂, and —CH(OMe)(OEt). Hemiacetal: —CH(OH)(OR¹), wherein R¹ is a hemiacetal substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of hemiacetal groups include, but are not limited to, —CH(OH)(OMe) and —CH(OH)(OEt). Ketal: —CR(OR¹)(OR²), where R¹ and R² are as defined for acetals, and R is a ketal substituent other than hydrogen, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples ketal groups include, but are not limited to, —C(Me)(OMe)₂, —C(Me)(OEt)₂, —C(Me)(OMe)(OEt), —C(Et)(OMe)₂, —C(Et)(OEt)₂, and —C(Et)(OMe)(OEt). Hemiketal: —CR(OH)(OR¹), where R¹ is as defined for hemiacetals, and R is a hemiketal substituent other than hydrogen, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of hemiacetal groups include, but are not limited to, —C(Me)(OH)(OMe), —C(Et)(OH)(OMe), —C(Me)(OH)(OEt), and —C(Et)(OH)(OEt). Oxo (keto, -one): ═O. Thione (thioketone): ═S. Imino (imine): ═NR, wherein R is an imino substituent, for example, hydrogen, C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, ═NH, ═NMe, ═NEt, and ═NPh. Formyl (carbaldehyde, carboxaldehyde): —C(═O)H. Acyl (keto): —C(═O)R, wherein R is an acyl substituent, for example, a C₁₋₇ alkyl group (also referred to as C₁₋₇ alkylacyl or C₁₋₇ alkanoyl), a C₃₋₂₀ heterocyclyl group (also referred to as C₃₋₂₀ heterocyclylacyl), or a C₅₋₂₀ aryl group (also referred to as C₅₋₂₀ arylacyl), preferably a C₁₋₇ alkyl group. Examples of acyl groups include, but are not limited to, —C(═O)CH₃ (acetyl), —C(═O)CH₂CH₃ (propionyl), —C(═O)C(CH₃)₃ (t-butyryl), and —C(═O)Ph (benzoyl, phenone). Carboxy (carboxylic acid): —C(═O)OH. Thiocarboxy (thiocarboxylic acid): —C(═S)SH. Thiolocarboxy (thiolocarboxylic acid): —C(═O)SH. Thionocarboxy (thionocarboxylic acid): —C(═S)OH. Imidic acid: —C(═NH)OH. Hydroxamic acid: —C(═NOH)OH. Ester (carboxylate, carboxylic acid ester, oxycarbonyl): —C(═O)OR, wherein R is an ester substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, —C(═O)OCH₃, —C(═O)OCH₂CH₃, —C(═O)OC(CH₃)₃, and —C(═O)OPh. Acyloxy (reverse ester): —OC(═O)R, wherein R is an acyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of acyloxy groups include, but are not limited to, —OC(═O)CH₃ (acetoxy), —OC(═O)CH₂CH₃, —OC(═O)C(CH₃)₃, —OC(═O)Ph, and —OC(═O)CH₂Ph. Oxycarboyloxy: —OC(═O)OR, wherein R is an ester substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of ester groups include, but are not limited to, —OC(═O)OCH₃, —OC(═O)OCH₂CH₃, —OC(═O)OC(CH₃)₃, and —OC(═O)OPh. Amino: —NR¹R², wherein R¹ and R² are independently amino substituents, for example, hydrogen, a C₁₋₇ alkyl group (also referred to as C₁₋₇ alkylamino or di-C₁₋₇alkylamino), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇ alkyl group, or, in the case of a “cyclic” amino group, R¹ and R², taken together with the nitrogen atom to which they are attached, form a heterocyclic ring having from 4 to 8 ring atoms. Amino groups may be primary (—NH₂), secondary (—NHR¹), or tertiary (—NHR¹R²), and in cationic form, may be quaternary (—⁺NR¹R²R³). Examples of amino groups include, but are not limited to, —NH₂, —NHCH₃, —NHC(CH₃)₂, —N(CH₃)₂, —N(CH₂CH₃)₂, and —NHPh. Examples of cyclic amino groups include, but are not limited to, aziridino, azetidino, pyrrolidino, piperidino, piperazino, morpholino, and thiomorpholino. Amido (carbamoyl, carbamyl, aminocarbonyl, carboxamide): —C(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(═O)NH₂, —C(═O)NHCH₃, —C(═O)N(CH₃)₂, —C(═O)NHCH₂CH₃, and —C(═O)N(CH₂CH₃)₂, as well as amido groups in which R¹ and R², together with the nitrogen atom to which they are attached, form a heterocyclic structure as in, for example, piperidinocarbonyl, morpholinocarbonyl, thiomorpholinocarbonyl, and piperazinocarbonyl. Thioamido (thiocarbamyl): —C(═S)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of amido groups include, but are not limited to, —C(═S)NH₂, —C(═S)NHCH₃, —C(═S)N(CH₃)₂, and —C(═S)NHCH₂CH₃. Acylamido (acylamino): —NR¹C(═O)R², wherein R¹ is an amide substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group, and R² is an acyl substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of acylamide groups include, but are not limited to, —NHC(═O)CH₃, —NHC(═O)CH₂CH₃, and —NHC(═O)Ph. R¹ and R² may together form a cyclic structure, as in, for example, succinimidyl, maleimidyl, and phthalimidyl:

Aminocarbonyloxy: —OC(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of aminocarbonyloxy groups include, but are not limited to, —OC(═O)NH₂, —OC(═O)NHMe, —OC(═O)NMe₂, and —OC(═O)NEt₂. Ureido: —N(R¹)CONR²R³ wherein R² and R³ are independently amino substituents, as defined for amino groups, and R¹ is a ureido substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably hydrogen or a C₁₋₇ alkyl group. Examples of ureido groups include, but are not limited to, —NHCONH₂, —NHCONHMe, —NHCONHEt, —NHCONMe₂, —NHCONEt₂, —NMeCONH₂, —NMeCONHMe, —NMeCONHEt, —NMeCONMe₂, and —NMeCONEt₂. Guanidino: —NH—C(═NH)NH₂. Tetrazolyl: a five membered aromatic ring having four nitrogen atoms and one carbon atom,

Imino: ═NR, wherein R is an imino substituent, for example, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇alkyl group. Examples of imino groups include, but are not limited to, ═NH, ═NMe, and ═NEt. Amidine (amidino): —C(═NR)NR₂, wherein each R is an amidine substituent, for example, hydrogen, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably H or a C₁₋₇ alkyl group. Examples of amidine groups include, but are not limited to, —C(═NH)NH₂, —C(═NH)NMe₂, and —C(═NMe)NMe₂. Nitro: —NO₂. Nitroso: —NO. Azido: —N₃. Cyano (nitrile, carbonitrile): —CN. Isocyano: —NC. Cyanato: —OCN. Isocyanato: —NCO. Thiocyano (thiocyanato): —SCN. Isothiocyano (isothiocyanato): —NCS. Sulfhydryl (thiol, mercapto): —SH. Thioether (sulfide): —SR, wherein R is a thioether substituent, for example, a C₁₋₇ alkyl group (also referred to as a C₁₋₇alkylthio group), a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of C₁₋₇ alkylthio groups include, but are not limited to, —SCH₃ and —SCH₂CH₃. Disulfide: —SS—R, wherein R is a disulfide substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group (also referred to herein as C₁₋₇ alkyl disulfide). Examples of C₁₋₇ alkyl disulfide groups include, but are not limited to, —SSCH₃ and —SSCH₂CH₃. Sulfine (sulfinyl, sulfoxide): —S(═O)R, wherein R is a sulfine substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfine groups include, but are not limited to, —S(═O)CH₃ and —S(═O)CH₂CH₃. Sulfone (sulfonyl): —S(═O)₂R, wherein R is a sulfone substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group, including, for example, a fluorinated or perfluorinated C₁₋₇ alkyl group. Examples of sulfone groups include, but are not limited to, —S(═O)₂CH₃ (methanesulfonyl, mesyl), —S(═O)₂CF₃ (triflyl), —S(═O)₂CH₂CH₃ (esyl), —S(═O)₂C₄F₉ (nonaflyl), —S(═O)₂CH₂CF₃ (tresyl), —S(═O)₂CH₂CH₂NH₂ (tauryl), —S(═O)₂Ph (phenylsulfonyl, besyl), 4-methylphenylsulfonyl (tosyl), 4-chlorophenylsulfonyl (closyl), 4-bromophenylsulfonyl (brosyl), 4-nitrophenyl (nosyl), 2-naphthalenesulfonate (napsyl), and 5-dimethylamino-naphthalen-1-ylsulfonate (dansyl). Sulfinic acid (sulfino): —S(═O)OH, —SO₂H. Sulfonic acid (sulfo): —S(═O)₂OH, —SO₃H. Sulfinate (sulfinic acid ester): —S(═O)OR; wherein R is a sulfinate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinate groups include, but are not limited to, —S(═O)OCH₃ (methoxysulfinyl; methyl sulfinate) and —S(═O)OCH₂CH₃ (ethoxysulfinyl; ethyl sulfinate). Sulfonate (sulfonic acid ester): —S(═O)₂OR, wherein R is a sulfonate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonate groups include, but are not limited to, —S(═O)₂OCH₃ (methoxysulfonyl; methyl sulfonate) and —S(═O)₂OCH₂CH₃ (ethoxysulfonyl; ethyl sulfonate). Sulfinyloxy: —OS(═O)R, wherein R is a sulfinyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinyloxy groups include, but are not limited to, —OS(═O)CH₃ and —OS(═O)CH₂CH₃. Sulfonyloxy: —OS(═O)₂R, wherein R is a sulfonyloxy substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonyloxy groups include, but are not limited to, —OS(═O)₂CH₃ (mesylate) and —OS(═O)₂CH₂CH₃ (esylate). Sulfate: —OS(═O)₂OR; wherein R is a sulfate substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfate groups include, but are not limited to, —OS(═O)₂OCH₃ and —SO(═O)₂OCH₂CH₃. Sulfamyl (sulfamoyl; sulfinic acid amide; sulfinamide): —S(═O)NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfamyl groups include, but are not limited to, —S(═O)NH₂, —S(═O)NH(CH₃), —S(═O)N(CH₃)₂, —S(═O)NH(CH₂CH₃), —S(═O)N(CH₂CH₃)₂, and —S(═O)NHPh. Sulfonamido (sulfinamoyl; sulfonic acid amide; sulfonamide): —S(═O)₂NR¹R², wherein R¹ and R² are independently amino substituents, as defined for amino groups. Examples of sulfonamido groups include, but are not limited to, —S(═O)₂NH₂, —S(═O)₂NH(CH₃), —S(═O)₂N(CH₃)₂, —S(═O)₂NH(CH₂CH₃), —S(═O)₂N(CH₂CH₃)₂, and —S(═O)₂NHPh. Sulfamino: —NR¹S(═O)₂OH, wherein R¹ is an amino substituent, as defined for amino groups. Examples of sulfamino groups include, but are not limited to, —NHS(═O)₂OH and —N(CH₃)S(═O)₂OH. Sulfonamino: —NR¹S(═O)₂R, wherein R¹ is an amino substituent, as defined for amino groups, and R is a sulfonamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfonamino groups include, but are not limited to, —NHS(═O)₂CH₃ and —N(CH₃)S(═O)₂C₆H₅. Sulfinamino: —NR¹S(═O)R, wherein R¹ is an amino substituent, as defined for amino groups, and R is a sulfinamino substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group. Examples of sulfinamino groups include, but are not limited to, —NHS(═O)CH₃ and —N(CH₃)S(═O)C₆H₅. Phosphino (phosphine): —PR₂, wherein R is a phosphino substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphino groups include, but are not limited to, —PH₂, —P(CH₃)₂, —P(CH₂CH₃)₂, —P(t-Bu)₂, and —P(Ph)₂. Phospho: —P(═O)₂. Phosphinyl (phosphine oxide): —P(═O)R₂, wherein R is a phosphinyl substituent, for example, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably a C₁₋₇ alkyl group or a C₅₋₂₀ aryl group. Examples of phosphinyl groups include, but are not limited to, —P(═O)(CH₃)₂, —P(═O)(CH₂CH₃)₂, —P(═O)(t-Bu)₂, and —P(═O)(Ph)₂. Phosphonic acid (phosphono): —P(═O)(OH)₂. Phosphonate (phosphono ester): —P(═O)(OR)₂, where R is a phosphonate substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphonate groups include, but are not limited to, —P(═O)(OCH₃)₂, —P(═O)(OCH₂CH₃)₂, —P(═O)(O-t-Bu)₂, and —P(═O)(OPh)₂. Phosphoric acid (phosphonooxy): —OP(═O)(OH)₂. Phosphate (phosphonooxy ester): —OP(═O)(OR)₂, where R is a phosphate substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphate groups include, but are not limited to, —OP(═O)(OCH₃)₂, —OP(═O)(OCH₂CH₃)₂, —OP(═O)(O-t-Bu)₂, and —OP(═O)(OPh)₂. Phosphorous acid: —OP(OH)₂. Phosphite: —OP(OR)₂, where R is a phosphite substituent, for example, —H, a C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphite groups include, but are not limited to, —OP(OCH₃)₂, —OP(OCH₂CH₃)₂, —OP(O-t-Bu)₂, and —OP(OPh)₂. Phosphoramidite: —OP(OR¹)—NR² ₂, where R¹ and R² are phosphoramidite substituents, for example, —H, a (optionally substituted) C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphoramidite groups include, but are not limited to, —OP(OCH₂CH₃)—N(CH₃)₂, —OP(OCH₂CH₃)—N(i-Pr)₂, and —OP(OCH₂CH₂CN)—N(i-Pr)₂. Phosphoramidate: —OP(═O)(OR¹)—NR² ₂, where R¹ and R² are phosphoramidate substituents, for example, —H, a (optionally substituted) C₁₋₇ alkyl group, a C₃₋₂₀ heterocyclyl group, or a C₅₋₂₀ aryl group, preferably —H, a C₁₋₇ alkyl group, or a C₅₋₂₀ aryl group. Examples of phosphoramidate groups include, but are not limited to, —OP(═O)(OCH₂CH₃)—N(CH₃)₂, —OP(═O)(OCH₂CH₃)—N(i-Pr)₂, and —OP(═O)(OCH₂CH₂CN)—N(i-Pr)₂. Alkylene C₃₋₁₂ alkylene: The term “C₃₋₁₂ alkylene”, as used herein, pertains to a bidentate moiety obtained by removing two hydrogen atoms, either both from the same carbon atom, or one from each of two different carbon atoms, of a hydrocarbon compound having from 3 to 12 carbon atoms (unless otherwise specified), which may be aliphatic or alicyclic, and which may be saturated, partially unsaturated, or fully unsaturated. Thus, the term “alkylene” includes the sub-classes alkenylene, alkynylene, cycloalkylene, etc., discussed below.

Examples of linear saturated C₃₋₁₂ alkylene groups include, but are not limited to, —(CH₂)_(n)— where n is an integer from 3 to 12, for example, —CH₂CH₂CH₂— (propylene), —CH₂CH₂CH₂CH₂— (butylene), —CH₂CH₂CH₂CH₂CH₂— (pentylene) and —CH₂CH₂CH₂CH—₂CH₂CH₂CH₂— (heptylene).

Examples of branched saturated C₃₋₁₂ alkylene groups include, but are not limited to, —CH(CH₃)CH₂—, —CH(CH₃)CH₂CH₂—, —CH(CH₃)CH₂CH₂CH₂—, —CH₂CH(CH₃)CH₂—, —CH₂CH(CH₃)CH₂CH₂—, —CH(CH₂CH₃)—, —CH(CH₂CH₃)CH₂—, and —CH₂CH(CH₂CH₃)CH₂—.

Examples of linear partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ alkenylene, and alkynylene groups) include, but are not limited to, —CH═CH—CH₂—, —CH₂—CH═CH₂—, —CH═CH—CH₂—CH₂—, —CH═CH—CH₂—CH₂—CH₂—, —CH═CH—CH═CH—, —CH═CH—CH═CH—CH₂—, —CH═CH—CH═CH—CH₂—CH₂—, —CH═CH—CH₂—CH═CH—, —CH═CH—CH₂—CH₂—CH═CH—, and —CH₂—C≡C—CH₂—.

Examples of branched partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ alkenylene and alkynylene groups) include, but are not limited to, —C(CH₃)═CH—, —C(CH₃)═CH—CH₂—, —CH═CH—CH(CH₃)— and —C≡C—CH(CH₃)—.

Examples of alicyclic saturated C₃₋₁₂ alkylene groups (C₃₋₁₂ cycloalkylenes) include, but are not limited to, cyclopentylene (e.g. cyclopent-1,3-ylene), and cyclohexylene (e.g. cyclohex-1,4-ylene).

Examples of alicyclic partially unsaturated C₃₋₁₂ alkylene groups (C₃₋₁₂ cycloalkylenes) include, but are not limited to, cyclopentenylene (e.g. 4-cyclopenten-1,3-ylene), cyclohexenylene (e.g. 2-cyclohexen-1,4-ylene; 3-cyclohexen-1,2-ylene; 2,5-cyclohexadien-1,4-ylene).

Oxygen protecting group: the term “oxygen protecting group” refers to a moiety which masks a hydroxy group, and these are well known in the art. A large number of suitable groups are described on pages 23 to 200 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference. Classes of particular interest include silyl ethers (e.g. TMS, TBDMS), substituted methyl ethers (e.g. THP) and esters (e.g. acetate).

Carbamate nitrogen protecting group: the term “carbamate nitrogen protecting group” pertains to a moiety which masks the nitrogen in the imine bond, and these are well known in the art. These groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 503 to 549 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Hemi-aminal nitrogen protecting group: the term “hemi-aminal nitrogen protecting group” pertains to a group having the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 633 to 647 as amide protecting groups of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference. Conjugates

The present invention provides Conjugates comprising a PBD dimer connected to a Ligand unit via a Linker unit. In one embodiment, the Linker unit includes a Stretcher unit (A), a Specificity unit (L¹), and a Spacer unit (L²). The Linker unit is connected at one end to the Ligand unit (L) and at the other end to the PBD dimer compound (D).

In one aspect, such a Conjugate is shown below in formula IIIa: L-(A¹ _(a)-L¹ _(s)-L² _(y)-D)_(p)  (IIIa)

-   -   wherein:     -   L is the Ligand unit; and     -   -A¹ _(a)-L¹ _(s)-L² _(y)- is a Linker unit (LU), wherein:     -   -A¹- is a Stretcher unit,     -   a is 1 or 2,     -   -L¹- is a Specificity unit,     -   s is an integer ranging from 0 to 12,     -   -L²- is a Spacer unit,     -   y is 0, 1 or 2;     -   -D is a PBD dimer; and     -   p is from 1 to 20.

In another aspect, such a Conjugate is shown below in formula IIIb:

Also illustrated as: L-(A¹ _(a)-L² _(y)(-L¹ _(s))-D)_(p)  (IIIb)

-   -   wherein:     -   L is the Ligand unit; and     -   -A¹ _(a)-L¹ _(s)(L² _(y))- is a Linker unit (LU), wherein:     -   -A¹- is a Stretcher unit linked to a Stretcher unit (L²),     -   a is 1 or 2,     -   -L¹- is a Specificity unit linked to a Stretcher unit (L²),     -   s is an integer ranging from 0 to 12,     -   -L²- is a Spacer unit,     -   y is 0, 1 or 2;     -   -D is a PBD dimer; and     -   p is from 1 to 20.         Preferences

The following preferences may apply to all aspects of the invention as described above, or may relate to a single aspect. The preferences may be combined together in any combination.

In one embodiment, the Conjugate has the formula: L-(A¹ _(a)-L¹ _(s)-L² _(y)-D)_(p) L-(A¹ _(a)-L_(s) ¹-D)_(p), L-(A¹-L¹-D)_(p) or L-(A¹-D)_(p) wherein L, A¹, a, L¹, s, L², D, y and p are as described above.

In one embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D), CBA is the Cell Binding Agent, L¹ is a Specificity         unit, A¹ is a Stretcher unit connecting L¹ to the Cell Binding         Agent, L² is a Spacer unit, which is a covalent bond, a         self-immolative group or together with —OC(═O)— forms a         self-immolative group, and L² optional. —OC(═O)— may be         considered as being part of L¹ or L², as appropriate.

In another embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below: CBA-A¹ _(a)-L¹ _(s)-L² _(y)-*

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D), CBA is the Cell Binding Agent, L¹ is a Specificity         unit, A¹ is a Stretcher unit connecting L¹ to the Cell Binding         Agent, L² is a Spacer unit which is a covalent bond or a         self-immolative group, and a is 1 or 2, s is 0, 1 or 2, and y is         0 or 1 or 2.

In the embodiments illustrated above, L¹ can be a cleavable Specificity unit, and may be referred to as a “trigger” that when cleaved activates a self-immolative group (or self-immolative groups) L², when a self-immolative group(s) is present. When the Specificity unit L¹ is cleaved, or the linkage (i.e., the covalent bond) between L¹ and L² is cleaved, the self-immolative group releases the Drug unit (D).

In another embodiment, the Ligand unit (L) is a Cell Binding Agent (CBA) that specifically binds to a target molecule on the surface of a target cell. An exemplary formula is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         (D), CBA is the Cell Binding Agent, L¹ is a Specificity unit         connected to L², A¹ is a Stretcher unit connecting L² to the         Cell Binding Agent, L² is a self-immolative group, and a is 1 or         2, s is 1 or 2, and y is 1 or 2.

In the various embodiments discussed herein, the nature of L¹ and L² can vary widely. These groups are chosen on the basis of their characteristics, which may be dictated in part, by the conditions at the site to which the conjugate is delivered. Where the Specificity unit L¹ is cleavable, the structure and/or sequence of L¹ is selected such that it is cleaved by the action of enzymes present at the target site (e.g., the target cell). L¹ units that are cleavable by changes in pH (e.g. acid or base labile), temperature or upon irradiation (e.g. photolabile) may also be used. L¹ units that are cleavable under reducing or oxidising conditions may also find use in the Conjugates.

In some embodiments, L¹ may comprise one amino acid or a contiguous sequence of amino acids. The amino acid sequence may be the target substrate for an enzyme.

In one embodiment, L¹ is cleavable by the action of an enzyme. In one embodiment, the enzyme is an esterase or a peptidase. For example, L¹ may be cleaved by a lysosomal protease, such as a cathepsin.

In one embodiment, L² is present and together with —CO(═O)— forms a self-immolative group or self-immolative groups. In some embodiments, —CO(═O)— also is a self-immolative group.

In one embodiment, where L¹ is cleavable by the action of an enzyme and L² is present, the enzyme cleaves the bond between L¹ and L², whereby the self-immolative group(s) release the Drug unit.

L¹ and L², where present, may be connected by a bond selected from:

-   -   —C(═O)NH—,     -   —CO(═O)—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OCO(═O)—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH, and     -   —O— (a glycosidic bond).

An amino group of L¹ that connects to L² may be the N-terminus of an amino acid or may be derived from an amino group of an amino acid side chain, for example a lysine amino acid side chain.

A carboxyl group of L¹ that connects to L² may be the C-terminus of an amino acid or may be derived from a carboxyl group of an amino acid side chain, for example a glutamic acid amino acid side chain.

A hydroxy group of L¹ that connects to L² may be derived from a hydroxy group of an amino acid side chain, for example a serine amino acid side chain.

In one embodiment, —CO(═O)— and L² together form the group:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to the L¹,         Y is —N(H)—, —O—, —C(═O)N(H)— or —CO(═O)—, and n is 0 to 3. The         phenylene ring is optionally substituted with one, two or three         substituents as described herein.

In one embodiment, Y is NH.

In one embodiment, n is 0 or 1. Preferably, n is 0.

Where Y is NH and n is 0, the self-immolative group may be referred to as a p-aminobenzylcarbonyl linker (PABC).

The self-immolative group will allow for release of the Drug unit (i.e., the asymmetric PBD) when a remote site in the linker is activated, proceeding along the lines shown below (for n=0):

-   -   where the asterisk indicates the attachment to the Drug, L* is         the activated form of the remaining portion of the linker and         the released Drug unit is not shown. These groups have the         advantage of separating the site of activation from the Drug.

In another embodiment, —CO(═O)— and L² together form a group selected from:

-   -   where the asterisk, the wavy line, Y, and n are as defined         above. Each phenylene ring is optionally substituted with one,         two or three substituents as described herein. In one         embodiment, the phenylene ring having the Y substituent is         optionally substituted and the phenylene ring not having the Y         substituent is unsubstituted.

In another embodiment, —CO(═O)— and L² together form a group selected from:

-   -   where the asterisk, the wavy line, Y, and n are as defined         above, E is O, S or NR, D is N, CH, or CR, and F is N, CH, or         CR.

In one embodiment, D is N.

In one embodiment, D is CH.

In one embodiment, E is O or S.

In one embodiment, F is CH.

In a preferred embodiment, the covalent bond between L¹ and L² is a cathepsin labile (e.g., cleavable) bond.

In one embodiment, L¹ comprises a dipeptide. The amino acids in the dipeptide may be any combination of natural amino acids and non-natural amino acids. In some embodiments, the dipeptide comprises natural amino acids. Where the linker is a cathepsin labile linker, the dipeptide is the site of action for cathepsin-mediated cleavage. The dipeptide then is a recognition site for cathepsin.

In one embodiment, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-,     -   -Val-Cit-,     -   -Phe-Cit-,     -   -Leu-Cit-,     -   -Ile-Cit-,     -   -Phe-Arg-, and     -   -Trp-Cit-;         where Cit is citrulline. In such a dipeptide, —NH— is the amino         group of X₁, and CO is the carbonyl group of X₂.

Preferably, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-, and     -   -Val-Cit-.

Most preferably, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is -Phe-Lys-, Val-Cit or -Val-Ala-.

Other dipeptide combinations of interest include:

-   -   -Gly-Gly-,     -   -Pro-Pro-, and     -   -Val-Glu-.

Other dipeptide combinations may be used, including those described by Dubowchik et al., which is incorporated herein by reference.

In one embodiment, the amino acid side chain is chemically protected, where appropriate. The side chain protecting group may be a group as discussed below. Protected amino acid sequences are cleavable by enzymes. For example, a dipeptide sequence comprising a Boc side chain-protected Lys residue is cleavable by cathepsin.

Protecting groups for the side chains of amino acids are well known in the art and are described in the Novabiochem Catalog. Additional protecting group strategies are set out in Protective groups in Organic Synthesis, Greene and Wuts.

Possible side chain protecting groups are shown below for those amino acids having reactive side chain functionality:

-   -   Arg: Z, Mtr, Tos;     -   Asn: Trt, Xan;     -   Asp: Bzl, t-Bu;     -   Cys: Acm, Bzl, Bzl-OMe, Bzl-Me, Trt;     -   Glu: Bzl, t-Bu;     -   Gln: Trt, Xan;     -   His: Boc, Dnp, Tos, Trt;     -   Lys: Boc, Z—Cl, Fmoc, Z;     -   Ser: BzI, TBDMS, TBDPS;     -   Thr: Bz;     -   Trp: Boc;     -   Tyr: BzI, Z, Z—Br.

In one embodiment, —X₂— is connected indirectly to the Drug unit. In such an embodiment, the Spacer unit L² is present.

In one embodiment, the dipeptide is used in combination with a self-immolative group(s) (the Spacer unit). The self-immolative group(s) may be connected to —X₂—.

Where a self-immolative group is present, —X₂— is connected directly to the self-immolative group. In one embodiment, —X₂— is connected to the group Y of the self-immolative group. Preferably the group —X₂—CO— is connected to Y, where Y is NH.

In one embodiment, —X₁— is connected directly to A¹. Preferably the group NH—X₁— (the amino terminus of X₁) is connected to A¹. A¹ may comprise the functionality —CO— thereby to form an amide link with —X₁—.

In one embodiment, L¹ and L² together with —OC(═O)— comprise the group —X₁—X₂-PABC-. The PABC group is connected directly to the Drug unit. In one example, the self-immolative group and the dipeptide together form the group -Phe-Lys-PABC-, which is illustrated below:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, and the wavy line indicates the point of attachment to the         remaining portion of L¹ or the point of attachment to A¹.         Preferably, the wavy line indicates the point of attachment to         A¹.

Alternatively, the self-immolative group and the dipeptide together form the group -Val-Ala-PABC-, which is illustrated below:

-   -   where the asterisk and the wavy line are as defined above.

In another embodiment, L¹ and L² together with —OC(═O)— represent:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to A¹, Y         is a covalent bond or a functional group, and E is a group that         is susceptible to cleavage thereby to activate a self-immolative         group.

E is selected such that the group is susceptible to cleavage, e.g., by light or by the action of an enzyme. E may be —NO₂ or glucuronic acid (e.g., β-glucuronic acid). The former may be susceptible to the action of a nitroreductase, the latter to the action of a β-glucuronidase.

The group Y may be a covalent bond.

The group Y may be a functional group selected from:

-   -   —C(═O)—     -   —NH—     -   —O—     -   —C(═O)NH—,     -   —CO(═O)—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OCO(═O)—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH—,     -   —NHC(═O)NH,     -   —C(═O)NHC(═O)—,     -   SO₂, and     -   —S—.

The group Y is preferably —NH—, —CH₂—, —O—, and —S—.

In some embodiments, L¹ and L² together with —OC(═O)— represent:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, the wavy line indicates the point of attachment to A, Y is         a covalent bond or a functional group and E is glucuronic acid         (e.g., β-glucuronic acid). Y is preferably a functional group         selected from —NH—.

In some embodiments, L¹ and L² together represent:

-   -   where the asterisk indicates the point of attachment to the         remainder of L² or the Drug unit, the wavy line indicates the         point of attachment to A¹, Y is a covalent bond or a functional         group and E is glucuronic acid (e.g., β-glucuronic acid). Y is         preferably a functional group selected from —NH—, —CH₂—, —O—,         and —S—.

In some further embodiments, Y is a functional group as set forth above, the functional group is linked to an amino acid, and the amino acid is linked to the Stretcher unit A¹. In some embodiments, amino acid is β-alanine. In such an embodiment, the amino acid is equivalently considered part of the Stretcher unit.

The Specificity unit L¹ and the Ligand unit are indirectly connected via the Stretcher unit.

L¹ and A¹ may be connected by a bond selected from:

-   -   —C(═O)NH—,     -   —CO(═O)—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OCO(═O)—,     -   —NHC(═O)O—,     -   —OC(═O)NH—, and     -   —NHC(═O)NH—.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the group A¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, the         wavy line indicates the point of attachment to the Ligand unit,         n is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the connection between the Ligand unit and A¹ is through a thiol residue of the Ligand unit and a maleimide group of A¹.

In one embodiment, the connection between the Ligand unit and A¹ is:

-   -   where the asterisk indicates the point of attachment to the         remaining portion of A¹, L¹, L² or D, and the wavy line         indicates the point of attachment to the remaining portion of         the Ligand unit. In this embodiment, the S atom is typically         derived from the Ligand unit.

In each of the embodiments above, an alternative functionality may be used in place of the malemide-derived group shown below:

-   -   where the wavy line indicates the point of attachment to the         Ligand unit as before, and the asterisk indicates the bond to         the remaining portion of the A¹ group, or to L¹, L² or D.

In one embodiment, the maleimide-derived group is replaced with the group:

-   -   where the wavy line indicates point of attachment to the Ligand         unit, and the asterisk indicates the bond to the remaining         portion of the A¹ group, or to L¹, L² or D.

In one embodiment, the maleimide-derived group is replaced with a group, which optionally together with a Ligand unit (e.g., a Cell Binding Agent), is selected from:

-   -   —C(═O)NH—,     -   —CO(═O)—,     -   —NHC(═O)—,     -   —OC(═O)—,     -   —OCO(═O)—,     -   —NHC(═O)O—,     -   —OC(═O)NH—,     -   —NHC(═O)NH—,     -   —NHC(═O)NH,     -   —C(═O)NHC(═O)—,     -   —S—,     -   —S—S—,     -   —CH₂C(═O)—     -   —C(═O)CH₂—,     -   ═N—NH—, and     -   —NH—N═.

Of these —C(═O)CH₂— may be preferred especially when the carbonyl group is bound to —NH—.

In one embodiment, the maleimide-derived group is replaced with a group, which optionally together with the Ligand unit, is selected from:

-   -   where the wavy line indicates either the point of attachment to         the Ligand unit or the bond to the remaining portion of the A¹         group, and the asterisk indicates the other of the point of         attachment to the Ligand unit or the bond to the remaining         portion of the A¹ group.

Other groups suitable for connecting L¹ to the Cell Binding Agent are described in WO 2005/082023.

In one embodiment, the Stretcher unit A¹ is present, the Specificity unit L¹ is present and Spacer unit L² is absent. Thus, L¹ and the Drug unit are directly connected via a bond. Equivalently in this embodiment, L² is a bond.

L¹ and D may be connected by a bond selected from:

-   -   —C(═O)N<,     -   —OC(═O)N<, and     -   —NHC(═O)N<,         where N< is part of D.

In one embodiment, L¹ and D are preferably connected by a bond:

-   -   —C(═O)N<.

In one embodiment, L¹ comprises a dipeptide and one end of the dipeptide is linked to D. As described above, the amino acids in the dipeptide may be any combination of natural amino acids and non-natural amino acids. In some embodiments, the dipeptide comprises natural amino acids. Where the linker is a cathepsin labile linker, the dipeptide is the site of action for cathepsin-mediated cleavage. The dipeptide then is a recognition site for cathepsin.

In one embodiment, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-,     -   -Val-Cit-,     -   -Phe-Cit-,     -   -Leu-Cit-,     -   -Ile-Cit-,     -   -Phe-Arg-, and     -   -Trp-Cit-;         where Cit is citrulline. In such a dipeptide, —NH— is the amino         group of X₁, and CO is the carbonyl group of X₂.

Preferably, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is selected from:

-   -   -Phe-Lys-,     -   -Val-Ala-,     -   -Val-Lys-,     -   -Ala-Lys-, and     -   -Val-Cit-.

Most preferably, the group —X₁—X₂— in dipeptide, —NH—X₁—X₂—CO—, is -Phe-Lys- or -Val-Ala-.

Other dipeptide combinations of interest include:

-   -   -Gly-Gly-,     -   -Pro-Pro-, and     -   -Val-Glu-.

Other dipeptide combinations may be used, including those described above.

In one embodiment, L¹-D is:

-NH—X₁—X₂—CO—N<*

-   -   where —NH—X₁—X₂—CO is the dipeptide, —N< is part of the Drug         unit, the asterisk indicates the points of attachment to the         remainder of the Drug unit, and the wavy line indicates the         point of attachment to the remaining portion of L¹ or the point         of attachment to A¹. Preferably, the wavy line indicates the         point of attachment to A¹.

In one embodiment, the dipeptide is valine-alanine and L¹-D is:

-   -   where the asterisks, —N< and the wavy line are as defined above.

In one embodiment, the dipeptide is phenylalnine-lysine and L¹-D is:

-   -   where the asterisks, —N< and the wavy line are as defined above.

In one embodiment, the dipeptide is valine-citrulline.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 8, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 7, preferably 3 to 7, most         preferably 3 or 7.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 8, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups A¹-L¹ is:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 8, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         S is a sulfur group of the Ligand unit, the wavy line indicates         the point of attachment to the rest of the Ligand unit, and n is         0 to 6. In one embodiment, n is 5.

In one embodiment, the group L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         S is a sulfur group of the Ligand unit, the wavy line indicates         the point of attachment to the remainder of the Ligand unit, and         n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         S is a sulfur group of the Ligand unit, the wavy line indicates         the point of attachment to the remainder of the Ligand unit, n         is 0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1         and m is 0 to 10, 1 to 8, preferably 4 to 8, most preferably 4         or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the Ligand         unit, n is 0 or 1, and m is 0 to 30. In a preferred embodiment,         n is 1 and m is 0 to 10, 1 to 7, preferably 4 to 8, most         preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, n is 0 or 1, and m is 0 to 30. In a         preferred embodiment, n is 1 and m is 0 to 10, 1 to 8,         preferably 4 to 8, most preferably 4 or 8.

In one embodiment, the groups L-A¹-L¹ are:

-   -   where the asterisk indicates the point of attachment to L² or D,         the wavy line indicates the point of attachment to the remainder         of the Ligand unit, n is 0 or 1, and m is 0 to 30. In a         preferred embodiment, n is 1 and m is 0 to 10, 1 to 8,         preferably 4 to 8, most preferably 4 or 8.

In one embodiment, the Stretcher unit is an acetamide unit, having the formula:

-CH₂—CO—N—*

-   -   where the asterisk indicates the point of attachment to the         remainder of the

Stretcher unit, L¹ or D, and the wavy line indicates the point of attachment to the Ligand unit.

Linker-Drugs

In other embodiments, Linker-Drug compounds are provided for conjugation to a Ligand unit. In one embodiment, the Linker-Drug compounds are designed for connection to a Cell Binding Agent.

In one embodiment, the Drug Linker compound has the formula:

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D, as defined above), G¹ is a Stretcher group (A¹) to form         a connection to a Ligand unit, L¹ is a Specificity unit, L² (a         Spacer unit) is a covalent bond or together with —OC(═O)— forms         a self-immolative group(s).

In another embodiment, the Drug Linker compound has the formula: G¹-L¹-L²-*

-   -   where the asterisk indicates the point of attachment to the Drug         unit (D), G¹ is a Stretcher unit (A¹) to form a connection to a         Ligand unit, L¹ is a Specificity unit, L² (a Spacer unit) is a         covalent bond or a self-immolative group(s).

L¹ and L² are as defined above. References to connection to A¹ can be construed here as referring to a connection to G¹.

In one embodiment, where L¹ comprises an amino acid, the side chain of that amino acid may be protected. Any suitable protecting group may be used. In one embodiment, the side chain protecting groups are removable with other protecting groups in the compound, where present. In other embodiments, the protecting groups may be orthogonal to other protecting groups in the molecule, where present.

Suitable protecting groups for amino acid side chains include those groups described in the Novabiochem Catalog 2006/2007. Protecting groups for use in a cathepsin labile linker are also discussed in Dubowchik et al.

In certain embodiments of the invention, the group L¹ includes a Lys amino acid residue. The side chain of this amino acid may be protected with a Boc or Alloc protected group. A Boc protecting group is most preferred.

The functional group G¹ forms a connecting group upon reaction with a Ligand unit (e.g., a cell binding agent.

In one embodiment, the functional group G¹ is or comprises an amino, carboxylic acid, hydroxy, thiol, or maleimide group for reaction with an appropriate group on the Ligand unit. In a preferred embodiment, G¹ comprises a maleimide group.

In one embodiment, the group G¹ is an alkyl maleimide group. This group is suitable for reaction with thiol groups, particularly cysteine thiol groups, present in the cell binding agent, for example present in an antibody.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 2, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 8, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, L²         or D, and n is 0 to 6. In one embodiment, n is 5.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 2, preferably 4 to 8, and most preferably 4         or 8.

In one embodiment, the group G¹ is:

-   -   where the asterisk indicates the point of attachment to L¹, n is         0 or 1, and m is 0 to 30. In a preferred embodiment, n is 1 and         m is 0 to 10, 1 to 8, preferably 4 to 8, and most preferably 4         or 8.

In each of the embodiments above, an alternative functionality may be used in place of the malemide group shown below:

-   -   where the asterisk indicates the bond to the remaining portion         of the G group.

In one embodiment, the maleimide-derived group is replaced with the group:

-   -   where the asterisk indicates the bond to the remaining portion         of the G group.

In one embodiment, the maleimide group is replaced with a group selected from:

-   -   —C(═O)OH,     -   —OH,     -   —NH₂,     -   —SH,     -   —C(═O)CH₂X, where X is Cl, Br or I,     -   —CHO,     -   —NHNH₂     -   —C≡CH, and     -   —N₃ (azide).

Of these, —C(═O)CH₂X may be preferred, especially when the carbonyl group is bound to —NH—.

In one embodiment, L¹ is present, and G¹ is —NH₂, —NHMe, —COOH, —OH or —SH.

In one embodiment, where L¹ is present, G¹ is —NH₂ or —NHMe. Either group may be the N-terminal of an L¹ amino acid sequence.

In one embodiment, L¹ is present and G¹ is —NH₂, and Cis an amino acid sequence —X₁—X₂—, as defined above.

In one embodiment, L¹ is present and G¹ is COOH. This group may be the C-terminal of an L¹ amino acid sequence.

In one embodiment, L¹ is present and G¹ is OH.

In one embodiment, L¹ is present and G¹ is SH.

The group G¹ may be convertable from one functional group to another. In one embodiment, L¹ is present and G¹ is —NH₂. This group is convertable to another group G¹ comprising a maleimide group. For example, the group —NH₂ may be reacted with an acids or an activated acid (e.g., N-succinimide forms) of those G¹ groups comprising maleimide shown above.

The group G¹ may therefore be converted to a functional group that is more appropriate for reaction with a Ligand unit.

As noted above, in one embodiment, L¹ is present and G¹ is —NH₂, —NHMe, —COOH, —OH or —SH. In a further embodiment, these groups are provided in a chemically protected form. The chemically protected form is therefore a precursor to the linker that is provided with a functional group.

In one embodiment, G¹ is —NH₂ in a chemically protected form. The group may be protected with a carbamate protecting group. The carbamate protecting group may be selected from the group consisting of:

-   -   Alloc, Fmoc, Boc, Troc, Teoc, Cbz and PNZ.

Preferably, where G¹ is —NH₂, it is protected with an Alloc or Fmoc group.

In one embodiment, where G¹ is —NH₂, it is protected with an Fmoc group.

In one embodiment, the protecting group is the same as the carbamate protecting group of the capping group.

In one embodiment, the protecting group is not the same as the carbamate protecting group of the capping group. In this embodiment, it is preferred that the protecting group is removable under conditions that do not remove the carbamate protecting group of the capping group.

The chemical protecting group may be removed to provide a functional group to form a connection to a Ligand unit. Optionally, this functional group may then be converted to another functional group as described above.

In one embodiment, the active group is an amine. This amine is preferably the N-terminal amine of a peptide, and may be the N-terminal amine of the preferred dipeptides of the invention.

The active group may be reacted to yield the functional group that is intended to form a connection to a Ligand unit.

In other embodiments, the Linker unit is a precursor to the Linker unit having an active group. In this embodiment, the Linker unit comprises the active group, which is protected by way of a protecting group. The protecting group may be removed to provide the Linker unit having an active group.

Where the active group is an amine, the protecting group may be an amine protecting group, such as those described in Green and Wuts.

The protecting group is preferably orthogonal to other protecting groups, where present, in the Linker unit.

In one embodiment, the protecting group is orthogonal to the capping group. Thus, the active group protecting group is removable whilst retaining the capping group. In other embodiments, the protecting group and the capping group is removable under the same conditions as those used to remove the capping group.

In one embodiment, the Linker unit is:

-   -   where the asterisk indicates the point of attachment to the Drug         unit, and the wavy line indicates the point of attachment to the         remaining portion of the Linker unit, as applicable or the point         of attachment to G¹. Preferably, the wavy line indicates the         point of attachment to G¹.

In one embodiment. the Linker unit is:

where the asterisk and the wavy line are as defined above.

Other functional groups suitable for use in forming a connection between L¹ and the Cell Binding Agent are described in WO 2005/082023.

Ligand Unit

The Ligand Unit may be of any kind, and include a protein, polypeptide, peptide and a non-peptidic agent that specifically binds to a target molecule. In some embodiments, the Ligand unit may be a protein, polypeptide or peptide. In some embodiments, the Ligand unit may be a cyclic polypeptide. These Ligand units can include antibodies or a fragment of an antibody that contains at least one target molecule-binding site, lymphokines, hormones, growth factors, or any other cell binding molecule or substance that can specifically bind to a target. The ligand Unit is also referred to herein as a “binding agent” or “targeting agent”.

The terms “specifically binds” and “specific binding” refer to the binding of an antibody or other protein, polypeptide or peptide to a predetermined molecule (e.g., an antigen). Typically, the antibody or other molecule binds with an affinity of at least about 1×10⁷ M⁻¹, and binds to the predetermined molecule with an affinity that is at least two-fold greater than its affinity for binding to a non-specific molecule (e.g., BSA, casein) other than the predetermined molecule or a closely-related molecule.

Examples of Ligand units include those agents described for use in WO 2007/085930, which is incorporated herein.

In some embodiments, the Ligand unit is a Cell Binding Agent that binds to an extracellular target on a cell. Such a Cell Binding Agent can be a protein, polypeptide, peptide or a non-peptidic agent. In some embodiments, the Cell Binding Agent may be a protein, polypeptide or peptide. In some embodiments, the Cell Binding Agent may be a cyclic polypeptide. The Cell Binding Agent also may be antibody or an antigen-binding fragment of an antibody. Thus, in one embodiment, the present invention provides an antibody-drug conjugate (ADC).

In one embodiment the antibody is a monoclonal antibody; chimeric antibody; humanized antibody; fully human antibody; or a single chain antibody. One embodiment the antibody is a fragment of one of these antibodies having biological activity. Examples of such fragments include Fab, Fab′, F(ab′)₂ and Fv fragments.

The antibody may be a diabody, a domain antibody (DAB) or a single chain antibody.

In one embodiment, the antibody is a monoclonal antibody.

Antibodies for use in the present invention include those antibodies described in WO 2005/082023 which is incorporated herein. Particularly preferred are those antibodies for tumour-associated antigens. Examples of those antigens known in the art include, but are not limited to, those tumour-associated antigens set out in WO 2005/082023. See, for instance, pages 41-55.

In some embodiments, the conjugates are designed to target tumour cells via their cell surface antigens. The antigens may be cell surface antigens which are either over-expressed or expressed at abnormal times or cell types. Preferably, the target antigen is expressed only on proliferative cells (preferably tumour cells); however this is rarely observed in practice. As a result, target antigens are usually selected on the basis of differential expression between proliferative and healthy tissue.

Antibodies have been raised to target specific tumour related antigens including:

-   -   Cripto, CD19, CD20, CD22, CD30, CD33, Glycoprotein NMB, CanAg,         Her2 (ErbB2/Neu), CD56 (NCAM), CD70, CD79, CD138, PSCA, PSMA         (prostate specific membrane antigen), BCMA, E-selectin, EphB2,         Melanotransferin, Muc16 and TMEFF2.

The Ligand unit is connected to the Linker unit. In one embodiment, the Ligand unit is connected to A, where present, of the Linker unit.

In one embodiment, the connection between the Ligand unit and the Linker unit is through a thioether bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through a disulfide bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through an amide bond.

In one embodiment, the connection between the Ligand unit and the Linker unit is through an ester bond.

In one embodiment, the connection between the Ligand unit and the Linker is formed between a thiol group of a cysteine residue of the Ligand unit and a maleimide group of the Linker unit.

The cysteine residues of the Ligand unit may be available for reaction with the functional group of the Linker unit to form a connection. In other embodiments, for example where the Ligand unit is an antibody, the thiol groups of the antibody may participate in interchain disulfide bonds. These interchain bonds may be converted to free thiol groups by e.g. treatment of the antibody with DTT prior to reaction with the functional group of the Linker unit.

In some embodiments, the cysteine residue is an introduced into the heavy or light chain of an antibody. Positions for cysteine insertion by substitution in antibody heavy or light chains include those described in Published U.S. Application No. 2007-0092940 and International Patent Publication WO2008070593, which are incorporated herein.

Methods of Treatment

The compounds of the present invention may be used in a method of therapy. Also provided is a method of treatment, comprising administering to a subject in need of treatment a therapeutically-effective amount of a compound of formula I. The term “therapeutically effective amount” is an amount sufficient to show benefit to a patient. Such benefit may be at least amelioration of at least one symptom. The actual amount administered, and rate and time-course of administration, will depend on the nature and severity of what is being treated. Prescription of treatment, e.g. decisions on dosage, is within the responsibility of general practitioners and other medical doctors.

A compound may be administered alone or in combination with other treatments, either simultaneously or sequentially dependent upon the condition to be treated. Examples of treatments and therapies include, but are not limited to, chemotherapy (the administration of active agents, including, e.g. drugs; surgery; and radiation therapy.

Pharmaceutical compositions according to the present invention, and for use in accordance with the present invention, may comprise, in addition to the active ingredient, i.e. a compound of formula I, a pharmaceutically acceptable excipient, carrier, buffer, stabiliser or other materials well known to those skilled in the art. Such materials should be non-toxic and should not interfere with the efficacy of the active ingredient. The precise nature of the carrier or other material will depend on the route of administration, which may be oral, or by injection, e.g. cutaneous, subcutaneous, or intravenous.

Pharmaceutical compositions for oral administration may be in tablet, capsule, powder or liquid form. A tablet may comprise a solid carrier or an adjuvant. Liquid pharmaceutical compositions generally comprise a liquid carrier such as water, petroleum, animal or vegetable oils, mineral oil or synthetic oil. Physiological saline solution, dextrose or other saccharide solution or glycols such as ethylene glycol, propylene glycol or polyethylene glycol may be included. A capsule may comprise a solid carrier such a gelatin.

For intravenous, cutaneous or subcutaneous injection, or injection at the site of affliction, the active ingredient will be in the form of a parenterally acceptable aqueous solution which is pyrogen-free and has suitable pH, isotonicity and stability. Those of relevant skill in the art are well able to prepare suitable solutions using, for example, isotonic vehicles such as Sodium Chloride Injection, Ringer's Injection, Lactated Ringer's Injection. Preservatives, stabilisers, buffers, antioxidants and/or other additives may be included, as required.

The Compounds and Conjugates can be used to treat proliferative disease and autoimmune disease. The term “proliferative disease” pertains to an unwanted or uncontrolled cellular proliferation of excessive or abnormal cells which is undesired, such as, neoplastic or hyperplastic growth, whether in vitro or in vivo.

Examples of proliferative conditions include, but are not limited to, benign, pre-malignant, and malignant cellular proliferation, including but not limited to, neoplasms and tumours (e.g., histocytoma, glioma, astrocyoma, osteoma), cancers (e.g. lung cancer, small cell lung cancer, gastrointestinal cancer, bowel cancer, colon cancer, breast carinoma, ovarian carcinoma, prostate cancer, testicular cancer, liver cancer, kidney cancer, bladder cancer, pancreatic cancer, brain cancer, sarcoma, osteosarcoma, Kaposi's sarcoma, melanoma), leukemias, psoriasis, bone diseases, fibroproliferative disorders (e.g. of connective tissues), and atherosclerosis. Other cancers of interest include, but are not limited to, haematological; malignancies such as leukemias and lymphomas, such as non-Hodgkin lymphoma, and subtypes such as DLBCL, marginal zone, mantle zone, and follicular, Hodgkin lymphoma, AML, and other cancers of B or T cell origin.

Examples of autoimmune disease include the following: rheumatoid arthritis, autoimmune demyelinative diseases (e.g., multiple sclerosis, allergic encephalomyelitis), psoriatic arthritis, endocrine ophthalmopathy, uveoretinitis, systemic lupus erythematosus, myasthenia gravis, Graves' disease, glomerulonephritis, autoimmune hepatological disorder, inflammatory bowel disease (e.g., Crohn's disease), anaphylaxis, allergic reaction, Sjögren's syndrome, type I diabetes mellitus, primary biliary cirrhosis, Wegener's granulomatosis, fibromyalgia, polymyositis, dermatomyositis, multiple endocrine failure, Schmidt's syndrome, autoimmune uveitis, Addison's disease, adrenalitis, thyroiditis, Hashimoto's thyroiditis, autoimmune thyroid disease, pernicious anemia, gastric atrophy, chronic hepatitis, lupoid hepatitis, atherosclerosis, subacute cutaneous lupus erythematosus, hypoparathyroidism, Dressler's syndrome, autoimmune thrombocytopenia, idiopathic thrombocytopenic purpura, hemolytic anemia, pemphigus vulgaris, pemphigus, dermatitis herpetiformis, alopecia arcata, pemphigoid, scleroderma, progressive systemic sclerosis, CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia), male and female autoimmune infertility, ankylosing spondolytis, ulcerative colitis, mixed connective tissue disease, polyarteritis nedosa, systemic necrotizing vasculitis, atopic dermatitis, atopic rhinitis, Goodpasture's syndrome, Chagas' disease, sarcoidosis, rheumatic fever, asthma, recurrent abortion, anti-phospholipid syndrome, farmer's lung, erythema multiforme, post cardiotomy syndrome, Cushing's syndrome, autoimmune chronic active hepatitis, bird-fancier's lung, toxic epidermal necrolysis, Alport's syndrome, alveolitis, allergic alveolitis, fibrosing alveolitis, interstitial lung disease, erythema nodosum, pyoderma gangrenosum, transfusion reaction, Takayasu's arteritis, polymyalgia rheumatica, temporal arteritis, schistosomiasis, giant cell arteritis, ascariasis, aspergillosis, Sampter's syndrome, eczema, lymphomatoid granulomatosis, Behcet's disease, Caplan's syndrome, Kawasaki's disease, dengue, encephalomyelitis, endocarditis, endomyocardial fibrosis, endophthalmitis, erythema elevatum et diutinum, psoriasis, erythroblastosis fetalis, eosinophilic faciitis, Shulman's syndrome, Felty's syndrome, filariasis, cyclitis, chronic cyclitis, heterochronic cyclitis, Fuch's cyclitis, IgA nephropathy, Henoch-Schonlein purpura, graft versus host disease, transplantation rejection, cardiomyopathy, Eaton-Lambert syndrome, relapsing polychondritis, cryoglobulinemia, Waldenstrom's macroglobulemia, Evan's syndrome, and autoimmune gonadal failure.

In some embodiments, the autoimmune disease is a disorder of B lymphocytes (e.g., systemic lupus erythematosus, Goodpasture's syndrome, rheumatoid arthritis, and type I diabetes), Th1-lymphocytes (e.g., rheumatoid arthritis, multiple sclerosis, psoriasis, Sjögren's syndrome, Hashimoto's thyroiditis, Graves' disease, primary biliary cirrhosis, Wegener's granulomatosis, tuberculosis, or graft versus host disease), or Th2-lymphocytes (e.g., atopic dermatitis, systemic lupus erythematosus, atopic asthma, rhinoconjunctivitis, allergic rhinitis, Omenn's syndrome, systemic sclerosis, or chronic graft versus host disease). Generally, disorders involving dendritic cells involve disorders of Th1-lymphocytes or Th2-lymphocytes. In some embodiments, the autoimmunie disorder is a T cell-mediated immunological disorder.

In some embodiments, the amount of the Conjugate administered ranges from about 0.01 to about 10 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.01 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.05 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 5 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 4 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.05 to about 3 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 3 mg/kg per dose. In some embodiments, the amount of the Conjugate administered ranges from about 0.1 to about 2 mg/kg per dose.

Includes Other Forms

Unless otherwise specified, included in the above are the well known ionic, salt, solvate, and protected forms of these substituents. For example, a reference to carboxylic acid (—COOH) also includes the anionic (carboxylate) form (—COO⁻), a salt or solvate thereof, as well as conventional protected forms. Similarly, a reference to an amino group includes the protonated form (—N⁺HR¹R²), a salt or solvate of the amino group, for example, a hydrochloride salt, as well as conventional protected forms of an amino group. Similarly, a reference to a hydroxyl group also includes the anionic form (—O⁻), a salt or solvate thereof, as well as conventional protected forms.

Salts

It may be convenient or desirable to prepare, purify, and/or handle a corresponding salt of the active compound, for example, a pharmaceutically-acceptable salt. Examples of pharmaceutically acceptable salts are discussed in Berge, et al., J. Pharm. Sci., 66, 1-19 (1977).

For example, if the compound is anionic, or has a functional group which may be anionic (e.g. —COOH may be —COO⁻), then a salt may be formed with a suitable cation. Examples of suitable inorganic cations include, but are not limited to, alkali metal ions such as Na⁺ and K⁺, alkaline earth cations such as Ca²⁺ and Mg²⁺, and other cations such as Al⁺³. Examples of suitable organic cations include, but are not limited to, ammonium ion (i.e. NH₄ ⁺) and substituted ammonium ions (e.g. NH₃R⁺, NH₂R₂ ⁺, NHR₃ ⁺, NR₄ ⁺). Examples of some suitable substituted ammonium ions are those derived from: ethylamine, diethylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH₃)₄ ⁺.

If the compound is cationic, or has a functional group which may be cationic (e.g. —NH₂ may be —NH₃ ⁺), then a salt may be formed with a suitable anion. Examples of suitable inorganic anions include, but are not limited to, those derived from the following inorganic acids: hydrochloric, hydrobromic, hydroiodic, sulfuric, sulfurous, nitric, nitrous, phosphoric, and phosphorous.

Examples of suitable organic anions include, but are not limited to, those derived from the following organic acids: 2-acetyoxybenzoic, acetic, ascorbic, aspartic, benzoic, camphorsulfonic, cinnamic, citric, edetic, ethanedisulfonic, ethanesulfonic, fumaric, glucheptonic, gluconic, glutamic, glycolic, hydroxymaleic, hydroxynaphthalene carboxylic, isethionic, lactic, lactobionic, lauric, maleic, malic, methanesulfonic, mucic, oleic, oxalic, palmitic, pamoic, pantothenic, phenylacetic, phenylsulfonic, propionic, pyruvic, salicylic, stearic, succinic, sulfanilic, tartaric, toluenesulfonic, and valeric. Examples of suitable polymeric organic anions include, but are not limited to, those derived from the following polymeric acids: tannic acid, carboxymethyl cellulose.

Solvates

It may be convenient or desirable to prepare, purify, and/or handle a corresponding solvate of the active compound. The term “solvate” is used herein in the conventional sense to refer to a complex of solute (e.g. active compound, salt of active compound) and solvent. If the solvent is water, the solvate may be conveniently referred to as a hydrate, for example, a mono-hydrate, a di-hydrate, a tri-hydrate, etc.

Carbinolamines

The invention includes compounds where a solvent adds across the imine bond of the PBD moiety, which is illustrated below where the solvent is water or an alcohol (R^(A)OH, where R^(A) is C₁₋₄ alkyl):

These forms can be called the carbinolamine and carbinolamine ether forms of the PBD. The balance of these equilibria depend on the conditions in which the compounds are found, as well as the nature of the moiety itself.

These particular compounds may be isolated in solid form, for example, by lyophilisation.

Isomers

Certain compounds may exist in one or more particular geometric, optical, enantiomeric, diasteriomeric, epimeric, atropic, stereoisomeric, tautomeric, conformational, or anomeric forms, including but not limited to, cis- and trans-forms; E- and Z-forms; c-, t-, and r-forms; endo- and exo-forms; R-, S-, and meso-forms; D- and L-forms; d- and I-forms; (+) and (−) forms; keto-, enol-, and enolate-forms; syn- and anti-forms; synclinal- and anticlinal-forms; α- and β-forms; axial and equatorial forms; boat-, chair-, twist-, envelope-, and halfchair-forms; and combinations thereof, hereinafter collectively referred to as “isomers” (or “isomeric forms”).

Note that, except as discussed below for tautomeric forms, specifically excluded from the term “isomers”, as used herein, are structural (or constitutional) isomers (i.e. isomers which differ in the connections between atoms rather than merely by the position of atoms in space). For example, a reference to a methoxy group, —OCH₃, is not to be construed as a reference to its structural isomer, a hydroxymethyl group, —CH₂OH. Similarly, a reference to ortho-chlorophenyl is not to be construed as a reference to its structural isomer, meta-chlorophenyl. However, a reference to a class of structures may well include structurally isomeric forms falling within that class (e.g. C₁₋₇ alkyl includes n-propyl and iso-propyl; butyl includes n-, iso-, sec-, and tert-butyl; methoxyphenyl includes ortho-, meta-, and para-methoxyphenyl).

The above exclusion does not pertain to tautomeric forms, for example, keto-, enol-, and enolate-forms, as in, for example, the following tautomeric pairs: keto/enol (illustrated below), imine/enamine, amide/imino alcohol, amidine/amidine, nitroso/oxime, thioketone/enethiol, N-nitroso/hyroxyazo, and nitro/aci-nitro.

Note that specifically included in the term “isomer” are compounds with one or more isotopic substitutions. For example, H may be in any isotopic form, including ¹H, ²H (D), and ³H (T); C may be in any isotopic form, including ¹²C, ¹³C, and ¹⁴C; O may be in any isotopic form, including ¹⁶O and ¹⁸O; and the like.

Unless otherwise specified, a reference to a particular compound includes all such isomeric forms, including (wholly or partially) racemic and other mixtures thereof. Methods for the preparation (e.g. asymmetric synthesis) and separation (e.g. fractional crystallisation and chromatographic means) of such isomeric forms are either known in the art or are readily obtained by adapting the methods taught herein, or known methods, in a known manner.

General Synthetic Routes

The synthesis of PBD compounds is extensively discussed in the following references, which discussions are incorporated herein by reference:

a) WO 00/12508 (pages 14 to 30);

b) WO 2005/023814 (pages 3 to 10);

c) WO 2004/043963 (pages 28 to 29); and

d) WO 2005/085251 (pages 30 to 39).

Synthesis Route

The compounds of the present invention, where R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, can be synthesised from a compound of Formula 2:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), R¹², X, X′ and R″ are as defined for compounds of formula I, Prot^(N) is a nitrogen protecting group for synthesis and Prot^(O) is a protected oxygen group for synthesis or an oxo group, by deprotecting the imine bond by standard methods. The compound produced may be in its carbinolamine or carbinolamine ether form depending on the solvents used. For example if Prot^(N) is Alloc and Prot^(O) is an oxygen protecting group for synthesis, then the deprotection is carried using palladium to remove the N10 protecting group, followed by the elimination of the oxygen protecting group for synthesis. If Prot^(N) is Troc and Prot^(O) is an oxygen protecting group for synthesis, then the deprotection is carried out using a Cd/Pb couple to yield the compound of formula (I). If Prot^(N) is SEM, or an analogous group, and Prot^(O) is an an oxo group, then the oxo group can be removed by reduction, which leads to a protected carbinolamine intermediate, which can then be treated to remove the SEM protecting group, followed by the elimination of water. The reduction of the compound of Formula 2 can be accomplished by, for example, lithium tetraborohydride, whilst a suitable means for removing the SEM protecting group is treatment with silica gel.

Compounds of formula 2 can be synthesised from a compound of formula 3a:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of formula 2, by coupling an organometallic derivative comprising R¹², such as an organoboron derivative. The organoboron derivative may be a boronate or boronic acid.

Compounds of formula 2 can be synthesised from a compound of formula 3b:

where R¹², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of formula 2, by coupling an organometallic derivative comprising R², such as an organoboron derivative. The organoboron derivative may be a boronate or boronic acid.

Compounds of formulae 3a and 3b can be synthesised from a compound of formula 4:

where R², R⁶, R⁷, R⁹, R^(6′), R^(7′), R^(9′), X, X′ and R″ are as defined for compounds of formula 2, by coupling about a single equivalent (e.g. 0.9 or 1 to 1.1 or 1.2) of an organometallic derivative, such as an organoboron derivative, comprising R² or R¹².

The couplings described above are usually carried out in the presence of a palladium catalyst, for example Pd(PPh₃)₄, Pd(OCOCH₃)₂, PdCl₂, Pd₂(dba)₃. The coupling may be carried out under standard conditions, or may also be carried out under microwave conditions.

The two coupling steps are usually carried out sequentially. They may be carried out with or without purification between the two steps. If no purification is carried out, then the two steps may be carried out in the same reaction vessel. Purification is usually required after the second coupling step. Purification of the compound from the undesired by-products may be carried out by column chromatography or ion-exchange separation.

The synthesis of compounds of formula 4 where Prot^(O) is an oxo group and Prot^(N) is SEM are described in detail in WO 00/12508, which is incorporated herein by reference. In particular, reference is made to scheme 7 on page 24, where the above compound is designated as intermediate P. This method of synthesis is also described in WO 2004/043963.

The synthesis of compounds of formula 4 where Prot^(O) is a protected oxygen group for synthesis are described in WO 2005/085251, which synthesis is herein incorporated by reference.

Compounds of formula I where R¹⁰ and R^(10′) are H and R¹¹ and R^(11′) are SO_(z)M, can be synthesised from compounds of formula I where R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, by the addition of the appropriate bisulphite salt or sulphinate salt, followed by an appropriate purification step. Further methods are described in GB 2 053 894, which is herein incorporated by reference.

Nitrogen Protecting Groups for Synthesis

Nitrogen protecting groups for synthesis are well known in the art. In the present invention, the protecting groups of particular interest are carbamate nitrogen protecting groups and hemi-aminal nitrogen protecting groups.

Carbamate nitrogen protecting groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 503 to 549 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Particularly preferred protecting groups include Troc, Teoc, Fmoc, BOC, Doc, Hoc, TcBOC, 1-Adoc and 2-Adoc.

Other possible groups are nitrobenzyloxycarbonyl (e.g. 4-nitrobenzyloxycarbonyl) and 2-(phenylsulphonyl)ethoxycarbonyl.

Those protecting groups which can be removed with palladium catalysis are not preferred, e.g. Alloc.

Hemi-aminal nitrogen protecting groups have the following structure:

wherein R′¹⁰ is R as defined above. A large number of suitable groups are described on pages 633 to 647 as amide protecting groups of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference. The groups disclosed herein can be applied to compounds of the present invention. Such groups include, but are not limited to, SEM, MOM, MTM, MEM, BOM, nitro or methoxy substituted BOM, Cl₃CCH₂OCH₂—. Protected Oxygen Group for Synthesis

Protected oxygen group for synthesis are well known in the art. A large number of suitable oxygen protecting groups are described on pages 23 to 200 of Greene, T. W. and Wuts, G. M., Protective Groups in Organic Synthesis, 3^(rd) Edition, John Wiley & Sons, Inc., 1999, which is incorporated herein by reference.

Classes of particular interest include silyl ethers, methyl ethers, alkyl ethers, benzyl ethers, esters, acetates, benzoates, carbonates, and sulfonates.

Preferred oxygen protecting groups include acetates, TBS and THP.

Synthesis of Drug Conjugates

Conjugates can be prepared as previously described. Linkers having a maleimidyl group (A), a peptide group (L¹) and self-immolative group (L²) can be prepared as described in U.S. Pat. No. 6,214,345, which is incorporated herein by reference. Linkers having a maleimidyl group (A) and a peptide group (L¹) can be prepared as described in WO 2009/0117531, which is incorporated herein by reference. Other linkers can be prepared according to the references cited herein or as known to the skilled artisan.

Linker-Drug compounds can be prepared according to methods known in the art. Linkage of amine-based X substituents (of the PDB dimer Drug unit) to active groups of the Linker units can be performed according to methods generally described in U.S. Pat. Nos. 6,214,345 and 7,498,298; and WO 2009-0117531, or as otherwise known to the skilled artisan.

Antibodies can be conjugated to Linker-Drug compounds as described in Doronina et al., Nature Biotechnology, 2003, 21, 778-784). Briefly, antibodies (4-5 mg/mL) in PBS containing 50 mM sodium borate at pH 7.4 are reduced with tris(carboxyethyl)phosphine hydrochloride (TCEP) at 37° C. The progress of the reaction, which reduces interchain disulfides, is monitored by reaction with 5,5′-dithiobis(2-nitrobenzoic acid) and allowed to proceed until the desired level of thiols/mAb is achieved. The reduced antibody is then cooled to 0° C. and alkylated with 1.5 equivalents of maleimide drug-linker per antibody thiol. After 1 hour, the reaction is quenched by the addition of 5 equivalents of N-acetyl cysteine. Quenched drug-linker is removed by gel filtration over a PD-10 column. The ADC is then sterile-filtered through a 0.22 μm syringe filter. Protein concentration can be determined by spectral analysis at 280 nm and 329 nm, respectively, with correction for the contribution of drug absorbance at 280 nm. Size exclusion chromatography can be used to determine the extent of antibody aggregation, and RP-HPLC can be used to determine the levels of remaining NAC-quenched drug-linker.

Antibodies with introduced cysteine residues can be conjugated to Linker-Drug compounds as described in International Patent Publication WO2008070593, which is incorporated herein or as follows. Antibodies containing an introduced cysteine residue in the heavy chain are fully reduced by adding 10 equivalents of TCEP and 1 mM EDTA and adjusting the pH to 7.4 with 1M Tris buffer (pH 9.0). Following a 1 hour incubation at 37° C., the reaction is cooled to 22° C. and 30 equivalents of dehydroascorbic acid is added to selectively reoxidize the native disulfides, while leaving the introduced cysteine in the reduced state. The pH is adjusted to 6.5 with 1M Tris buffer (pH 3.7) and the reaction is allowed to proceed for 1 hour at 22° C. The pH of the solution is then raised again to 7.4 by addition of 1 M Tris buffer (pH 9.0). 3.5 equivalents of the PBD drug linker in DMSO is placed in a suitable container for dilution with propylene glycol prior to addition to the reaction. To maintain solubility of the PBD drug linker, the antibody itself is first diluted with propylene glycol to a final concentration of 33% (e.g., if the antibody solution was in a 60 mL reaction volume, 30 mL of propylene glycol was added). This same volume of propylene glycol (30 mL in this example) is added to the PBD drug linker as a diluent. After mixing, the solution of PBD drug linker in propylene glycol is added to the antibody solution to effect the conjugation; the final concentration of propylene glycol is 50%. The reaction is allowed to proceed for 30 minutes and then quenched by addition of 5 equivalents of N-acetyl cysteine. The ADC is purified by ultrafiltration through a 30 kD membrane. (Note that the concentration of propylene glycol used in the reaction can be reduced for any particular PBD, as its sole purpose is to maintain solubility of the drug linker in the aqueous media.)

For halo-acetamide-based Linker-Drug compounds, conjugation can be performed generally as follows. To a solution of reduced and reoxidized antibodies (having introduced cysteines in the heavy chain) in 10 mM Tris (pH 7.4), 50 mM NaCl, and 2 mM DTPA is added 0.5 volumes of propylene glycol. A 10 mM solution of acetamide-based Linker-Drug compound in dimethylacetamide is prepared immediately prior to conjugation. An equivalent amount of propylene glycol as added to the antibody solution is added to a 6-fold molar excess of the Linker-Drug compound. The dilute Linker-Drug solution is added to the antibody solution and the pH is adjusted to 8-8.5 using 1 M Tris (pH 9). The conjugation reaction is allowed to proceed for 45 minutes at 37° C. The conjugation is verified by reducing and denaturing reversed phase PLRP-S chromatography. Excess Linker-Drug compound is removed with Quadrasil MP resin and the buffer is exchanged into 10 mM Tris (pH 7.4), 50 mM NaCl, and 5% propylene glycol using a PD-10 desalting column.

Illustrative Synthesis Schemes for Drug Linkers

The following schemes are illustrative of routes for synthesising drug linkers—the PBD dimer is shown with specific substituents, and dimer links, but these may be varied within the scope of the present invention.

The glucuronide linker intermediate S1 (reference: Jeffrey et al., Bioconjugate Chemistry, 2006, 17, 831-840) can be treated with diphosgene in dichlroromethane at −78° C. to afford the glucuronide chloroformate, which is then reacted with the PBD dimer S2 dissolved in CH₂Cl₂ by dropwise addition. Warming the reaction to 0° C. over 2 hours followed by extraction will yield the compound S3. Treating a solution of S3 in an equal solvent mixture of MeOH, tetrahydrofuran, and water (cooled to 0° C.) with lithium hydroxide monohydrate for 4 hours, followed by reaction with glacial acetic acid will yield the compound S4. Adding maleimidocaproyl NHS ester to a solution of S4 in DMF, followed by diisopropylethylamine and stirring at room temperature under nitrogen for 2 hours will yield the desired drug linker S5.

The maleimide linker S6, which can be synthesised by reacting maleimidocaproyl N-hydroxysuccinimide and H-Val-Ala-OH, can be linked to the exemplary compounds, S2, in the presence of EEDQ in anhydrous dichloromethane.

The linker S8 can be linked to the exemplary compounds, S2, in the presence of EEDQ in 5% methanol/dichloromethane. The deprotection of S9 can be carried out with the use of Ph₃P, pyrollidine and tetrakis palladium in anhydrous dichloromethane. S10 can be converted to the desired products by adding maleimidocaproyl-NHS ester, in the presence of DIPEA in DMF.

Further Preferences

The following preferences may apply to all aspects of the invention as described above, or may relate to a single aspect. The preferences may be combined together in any combination.

In some embodiments, R^(6′), R^(7′), R^(9′), R^(10′), R^(11′) and Y′ are preferably the same as R⁶, R⁷, R⁹, R¹⁰, R¹¹ and Y respectively.

Dimer Link

Y and Y′ are preferably 0.

R″ is preferably a C₃₋₇ alkylene group with no substituents. More preferably R″ is a C₃, C₅ or C₇ alkylene. Most preferably, R″ is a C₃ or C₅ alkylene.

R⁶ to R⁹

R⁹ is preferably H.

R⁶ is preferably selected from H, OH, OR, SH, NH₂, nitro and halo, and is more preferably H or halo, and most preferably is H.

R⁷ is preferably selected from H, OH, OR, SH, SR, NH₂, NHR, NRR′, and halo, and more preferably independently selected from H, OH and OR, where R is preferably selected from optionally substituted C₁₋₇ alkyl, C₃₋₁₀ heterocyclyl and C₅₋₁₀ aryl groups. R may be more preferably a C₁ alkyl group, which may or may not be substituted. A substituent of interest is a C₅₋₆ aryl group (e.g. phenyl). Particularly preferred substituents at the 7-positions are OMe and OCH₂Ph. Other substituents of particular interest are dimethylamino (i.e. —NMe₂); —(OC₂H₄)_(q)OMe, where q is from 0 to 2; nitrogen-containing C₆ heterocyclyls, including morpholino, piperidinyl and N-methyl-piperazinyl.

These preferences apply to R^(9′), R^(6′) and R^(7′) respectively.

R²

A in R² may be phenyl group or a C₅₋₇ heteroaryl group, for example furanyl, thiophenyl and pyridyl. In some embodiments, A is preferably phenyl. In other embodiments, A is preferably thiophenyl, for example, thiophen-2-yl and thiophen-3-yl.

X is a group selected from the list comprising: NHNH₂, CONHNH₂,

In some embodiments, X may be preferably selected from NHNH₂ and CONHNH₂. In other embodiments, X may be preferably selected from

Q²-X may be on any of the available ring atoms of the C₅₋₇ aryl group, but is preferably on a ring atom that is not adjacent the bond to the remainder of the compound, i.e. it is preferably β or γ to the bond to the remainder of the compound. Therefore, where the C₅₋₇ aryl group (A) is phenyl, the substituent (Q²-X) is preferably in the meta- or para-positions, and more preferably is in the para-position.

In some embodiments, Q¹ is a single bond. In these embodiments, Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and is from 1 to 3. In some of these embodiments, Q² is a single bond. In other embodiments, Q² is —Z—(CH₂)_(n)—. In these embodiments, Z may be O or S and n may be 1 or n may be 2. In other of these embodiments, Z may be a single bond and n may be 1.

In other embodiments, Q¹ is —CH═CH—.

In some embodiments, R² may be -A-CH₂—X and -A-X. In these embodiments, X may be

In particularly preferred embodiments, X may be

R¹²

R¹² may be a C₅₋₇ aryl group. A C₅₋₇ aryl group may be a phenyl group or a C₅₋₇ heteroaryl group, for example furanyl, thiophenyl and pyridyl. In some embodiments, R¹² is preferably phenyl. In other embodiments, R¹² is preferably thiophenyl, for example, thiophen-2-yl and thiophen-3-yl.

R¹² may be a C₈₋₁₀ aryl, for example a quinolinyl or isoquinolinyl group. The quinolinyl or isoquinolinyl group may be bound to the PBD core through any available ring position. For example, the quinolinyl may be quinolin-2-yl, quinolin-3-yl, quinolin-4yl, quinolin-5-yl, quinolin-6-yl, quinolin-7-yl and quinolin-8-yl. Of these quinolin-3-yl and quinolin-6-yl may be preferred. The isoquinolinyl may be isoquinolin-1-yl, isoquinolin-3-yl, isoquinolin-4yl, isoquinolin-5-yl, isoquinolin-6-yl, isoquinolin-7-yl and isoquinolin-8-yl. Of these isoquinolin-3-yl and isoquinolin-6-yl may be preferred.

R¹² may bear any number of substituent groups. It preferably bears from 1 to 3 substituent groups, with 1 and 2 being more preferred, and singly substituted groups being most preferred. The substituents may be any position.

Where R¹² is C₅₋₇ aryl group, a single substituent is preferably on a ring atom that is not adjacent the bond to the remainder of the compound, i.e. it is preferably β or γ to the bond to the remainder of the compound. Therefore, where the C₅₋₇ aryl group is phenyl, the substituent is preferably in the meta- or para-positions, and more preferably is in the para-position.

Where R¹² is a C₈₋₁₀ aryl group, for example quinolinyl or isoquinolinyl, it may bear any number of substituents at any position of the quinoline or isoquinoline rings. In some embodiments, it bears one, two or three substituents, and these may be on either the proximal and distal rings or both (if more than one substituent).

R¹² Substituents

If a substituent on R¹² is halo, it is preferably F or Cl, more preferably Cl.

If a substituent on R¹² is ether, it may in some embodiments be an alkoxy group, for example, a C₁₋₇ alkoxy group (e.g. methoxy, ethoxy) or it may in some embodiments be a C₅₋₇ aryloxy group (e.g phenoxy, pyridyloxy, furanyloxy). The alkoxy group may itself be further substituted, for example by an amino group (e.g. dimethylamino).

If a substituent on R¹² is C₁₋₇ alkyl, it may preferably be a C₁₋₄ alkyl group (e.g. methyl, ethyl, propryl, butyl).

If a substituent on R¹² is C₃₋₇ heterocyclyl, it may in some embodiments be C₆ nitrogen containing heterocyclyl group, e.g. morpholino, thiomorpholino, piperidinyl, piperazinyl. These groups may be bound to the rest of the PBD moiety via the nitrogen atom. These groups may be further substituted, for example, by C₁₋₄ alkyl groups. If the C₆ nitrogen containing heterocyclyl group is piperazinyl, the said further substituent may be on the second nitrogen ring atom.

If a substituent on R¹² is bis-oxy-C₁₋₃ alkylene, this is preferably bis-oxy-methylene or bis-oxy-ethylene.

Particularly preferred substituents for R¹² include methoxy, ethoxy, fluoro, chloro, cyano, bis-oxy-methylene, methyl-piperazinyl, morpholino and methyl-thiophenyl. Another particularly preferred substituent for R¹² is dimethylaminopropyloxy.

R¹² Groups

Particularly preferred substituted R¹² groups include, but are not limited to, 4-methoxy-phenyl, 3-methoxyphenyl, 4-ethoxy-phenyl, 3-ethoxy-phenyl, 4-fluoro-phenyl, 4-chloro-phenyl, 3,4-bisoxymethylene-phenyl, 4-methylthiophenyl, 4-cyanophenyl, 4-phenoxyphenyl, quinolin-3-yl and quinolin-6-yl, isoquinolin-3-yl and isoquinolin-6-yl, 2-thienyl, 2-furanyl, methoxynaphthyl, and naphthyl. Another possible substituted R¹² group is 4-nitrophenyl.

M and z

It is preferred that M and M′ are monovalent pharmaceutically acceptable cations, and are more preferably Na⁺.

z is preferably 3.

Particularly preferred compounds of the present invention are of formula Ia:

where n is 1 or 3; R^(1a) is methyl or phenyl; R^(12a) is selected from: (a)

and (b)

3^(rd) Aspect

The preferences expressed above for the first aspect may apply to the compounds of this aspect, where appropriate.

When R¹⁰ is carbamate nitrogen protecting group, it may preferably be Teoc, Fmoc and Troc, and may more preferably be Troc.

When R¹¹ is O-Prot^(O), wherein Prot^(O) is an oxygen protecting group, Prot^(O) may preferably be TBS or THP, and may more preferably be TBS.

When R¹⁰ is a hemi-aminal nitrogen protecting group, it may preferably be MOM, BOM or SEM, and may more preferably be SEM.

The preferences for compounds of formula I apply as appropriate to D in the sixth aspect of the invention.

EXAMPLES General Experimental Methods

Optical rotations were measured on an ADP 220 polarimeter (Bellingham Stanley Ltd.) and concentrations (c) are given in g/100 mL. Melting points were measured using a digital melting point apparatus (Electrothermal). IR spectra were recorded on a Perkin-Elmer Spectrum 1000 FT IR Spectrometer. ¹H and ¹³C NMR spectra were acquired at 300 K using a Bruker Avance NMR spectrometer at 400 and 100 MHz, respectively. Chemical shifts are reported relative to TMS (δ=0.0 ppm), and signals are designated as s (singlet), d (doublet), t (triplet), dt (double triplet), dd (doublet of doublets), ddd (double doublet of doublets) or m (multiplet), with coupling constants given in Hertz (Hz). Mass spectroscopy (MS) data were collected using a Waters Micromass ZQ instrument coupled to a Waters 2695 HPLC with a Waters 2996 PDA. Waters Micromass ZQ parameters used were: Capillary (kV), 3.38; Cone (V), 35; Extractor (V), 3.0; Source temperature (° C.), 100; Desolvation Temperature (° C.), 200; Cone flow rate (L/h), 50; De-solvation flow rate (L/h), 250. High-resolution mass spectroscopy (HRMS) data were recorded on a Waters Micromass QTOF Global in positive W-mode using metal-coated borosilicate glass tips to introduce the samples into the instrument. Thin Layer Chromatography (TLC) was performed on silica gel aluminium plates (Merck 60, F₂₅₄), and flash chromatography utilised silica gel (Merck 60, 230-400 mesh ASTM). Except for the HOBt (NovaBiochem) and solid-supported reagents (Argonaut), all other chemicals and solvents were purchased from Sigma-Aldrich and were used as supplied without further purification. Anhydrous solvents were prepared by distillation under a dry nitrogen atmosphere in the presence of an appropriate drying agent, and were stored over 4 Å molecular sieves or sodium wire. Petroleum ether refers to the fraction boiling at 40-60° C.

Compound 1 was synthesised as described in WO 2010/043880 (Compound 17), which is herein incorporated by reference.

General LC/MS conditions: The HPLC (Waters Alliance 2695) was run using a mobile phase of water (A) (formic acid 0.1%) and acetonitrile (B) (formic acid 0.1%). Gradient: initial composition 5% B over 1.0 min then 5% B to 95% B within 3 min. The composition was held for 0.5 min at 95% B, and then returned to 5% B in 0.3 minutes. Total gradient run time equals 5 min. Flow rate 3.0 mL/min, 400 μL was split via a zero dead volume tee piece which passes into the mass spectrometer. Wavelength detection range: 220 to 400 nm. Function type: diode array (535 scans). Column: Phenomenex® Onyx Monolithic C18 50×4.60 mm

Example 1

(a) Benzyl 4-(4-((S)-7-methoxy-8-(3-(((S)-7-methoxy-2-(4-methoxyphenyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-benzo[e]pyrrolo[1,2-a][1,4]diazepin-8-yl)oxy)propoxy)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-benzo[e]pyrrolo[1,2-a][1,4]diazepin-2-yl)phenyl)piperazine-1-carboxylate (3)

(S)-2-(4-methoxyphenyl)-7-methoxy-8-(3-((S)-7-methoxy-2-(trifluoromethylsulphonyl)-5,11-dioxo-10-((2-(trimethylsilyl)ethoxy)methyl)-5,10,11,11a-tetrahydro-1H-pyrrolo[2,1-c][1,4]benzodiazepin-8-yloxy)propyloxy)-10-((2-(trimethylsilyl)ethoxy)methyl)-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (1-Compound 17 in WO 2010/043880)(0.093 g, 0.086 mmol), benzyl 4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)piperazine-1-carboxylate (2)(0.047 g, 0.110 mmol, 1.3 eq) and sodium carbonate (0.009 g, 0.140 mmol, 1.5 eq) were suspended in ethanol (1.5 mL), toluene (3 mL) and water (1.5 mL) under an argon atmosphere. Pd(PPh₃)₄ (0.002 g, 0.002 mmol, 0.02 eq) was added to the mixture, and the reaction was stirred overnight at room temperature. EtOAc (10 mL) was added to the mixture and the organic phase was washed with brine (15 mL) and dried over MgSO₄, and the solvent was removed by rotary evaporation under reduced pressure. The crude was purified by flash column chromatography (silica gel, gradient 20% EtOAc/80% hexane-100% EtOAc). Compound 3 was obtained as a yellow solid (0.0549 g, 52%); Rf 0.21 [50% EtOAc-50% hexane]; LC-MS (5 min) 3.92 min, ES⁺ 1221.39.

(b) The desired compound A above could be synthesised from compound 3 by removal of the Cbz protecting group and reduction of the SEM dilactam as described above.

Example 2 Determination of In Vitro Cytotoxicity

K562 human chronic myeloid leukaemia cells were maintained in RPM1 1640 medium supplemented with 10% fetal calf serum and 2 mM glutamine at 37° C. in a humidified atmosphere containing 5% CO₂ and were incubated with a specified dose of drug for 96 hours at 37° C. in the dark. The incubation was terminated by centrifugation (5 min, 300 g) and the cells were washed once with drug-free medium. Following the appropriate drug treatment, the cells were transferred to 96-well microtiter plates (10⁴ cells per well, 8 wells per sample). Plates were then kept in the dark at 37° C. in a humidified atmosphere containing 5% CO₂. The assay is based on the ability of viable cells to reduce a yellow soluble tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT, Aldrich-Sigma), to an insoluble purple formazan precipitate. Following incubation of the plates for 4 days (to allow control cells to increase in number by approximately 10 fold), 20 μL of MTT solution (5 mg/mL in phosphate-buffered saline) was added to each well and the plates further incubated for 5 hours. The plates were then centrifuged for 5 minutes at 300 g and the bulk of the medium pipetted from the cell pellet leaving 10-20 μL per well. DMSO (200 μL) was added to each well and the samples agitated to ensure complete mixing. The optical density was then read at a wavelength of 550 nm on a Titertek Multiscan ELISA plate reader, and a dose-response curve was constructed. For each curve, an IC₅₀ value was read as the dose required to reduce the final optical density to 50% of the control value. 

The invention claimed is:
 1. A compound with the formula I:

wherein: R² is of formula II:

where A is phenyl, naphthyl or a C₅₋₇ heteroaryl group, X is selected from the group consisting of: NHNH₂, CONHNH₂,

and either: (i) Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is a phenyl, naphthyl, or C₅₋₁₀ heteroaryl group, optionally substituted by one or more substituents selected from the group consisting of: halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are H; R⁷ is a C₁₋₄ alkoxy, optionally substituted by a C₅ heteroaryl or phenyl group either: (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), where R^(A) is C₁₋₄ alkyl; (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R¹⁰ is H and R¹¹ is SO_(z)M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more aromatic rings; Y and Y′ are selected from O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation, wherein the term C₃₋₇ heterocyclyl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heterocyclic compounds which has from 3 to 7 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S, wherein the term C₅₋₁₀ heteroaryl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heteroaromatic compound which has from 5 to 10 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S.
 2. A compound according to claim 1, wherein Y is O, and R″ is C₃₋₇ alkylene.
 3. A compound according to claim 1, wherein A is phenyl, and X is selected from: (a) and

(b) NHNH₂ and CONHNH₂.
 4. A compound according to claim 1, wherein Q¹ is a single bond; and Q² is: (a) a single bond; or (b) —Z—(CH₂)_(n)—, Z is O or S and n is 1 or
 2. 5. A compound according to claim 1, wherein R² is -A-X, and X is


6. A compound according to claim 1, wherein R¹² is phenyl, which bears one to three substituent groups, selected from methoxy, ethoxy, fluoro, chloro, cyano, bis-oxy-methylene, methyl-piperazinyl, morpholino and methyl-thiophenyl.
 7. A compound according to claim 1, wherein R^(6′), R^(7′), R^(9′), R^(10′), R^(11″) and Y′ are the same as R⁶, R⁷, R⁹, R¹⁰, R¹¹ and Y respectively.
 8. A compound of formula II:

wherein: R² is of formula II:

where A is phenyl or a C₅₋₇ heteroaryl group, X is selected from the group consisting of: NHNH₂, CONHNH₂,

and either: (i) Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is phenyl, naphthyl or a C₅₋₁₀ heteroaryl group, optionally substituted by one or more substituents selected from the group consisting of: halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are H; R⁷ is a C₁₋₄ alkoxy, optionally substituted by a C₅ heteroaryl or phenyl group; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more aromatic rings; Y and Y′ are selected from O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation; and either: (a) R¹⁰ is carbamate nitrogen protecting group, and R¹¹ is O-Prot^(O), wherein Prot^(O) is an oxygen protecting group; (b) R¹⁰ is a hemi-aminal nitrogen protecting group and R¹¹ is an oxo group; and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein the term C₃₋₇ heterocyclyl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heterocyclic compounds which has from 3 to 7 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S, wherein the term C₅₋₁₀ heteroaryl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heteroaromatic compound which has from 5 to 10 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S.
 9. A compound according to claim 8, wherein R¹⁰ is Troc and R¹¹ is OTBS.
 10. A compound according to claim 8, wherein R¹¹ is oxo and R¹⁰ is SEM.
 11. A Conjugate having formula III: L-(LU-D)_(p)  (III) wherein L is a Ligand unit selected from an antibody and an antigen-binding fragment of an antibody, LU is a Linker unit which is A¹-L¹ , wherein A¹ is selected from:

where the asterisk indicates the point of attachment to L¹, the wavy line indicates the point of attachment to the Ligand unit, and n is 0 to 6;

where the asterisk indicates the point of attachment to L¹, the wavy line indicates the point of attachment to the Ligand unit, and n is 0 to 6;

where the asterisk indicates the point of attachment to L¹, the wavy line indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to 30; or

where the asterisk indicates the point of attachment to L¹, the wavy line indicates the point of attachment to the Ligand unit, n is 0 or 1, and m is 0 to 30; wherein the above formulae the maleimide-derived group may be replaced by —NH—C(O)—CH₂—; and L¹ selected from an amino acid sequence which is cleavable by the action of an enzyme, p is 1 to 20; and D is a Drug unit with the formula I:

wherein: R² is of formula II:

where A is phenyl, naphthyl or a C₅₋₇ heteroaryl group, X is selected from the group consisting of: *NHNH^(q), *CONHNH^(q),

where * indicates where the group is bound to the PBD moiety, and q indicates where the group is bound to the Linker Unit and either: (i) Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is a phenyl, naphthyl, or C₅₋₁₀ heteroaryl group, optionally substituted by one or more substituents selected from the group consisting of: halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are H; R⁷ is a C₁₋₄ alkoxy, optionally substituted by a C₅ heteroaryl or phenyl group; either: (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), where R^(A) is C₁₋₄ alkyl; (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R¹⁰ is H and R¹¹ is SO_(z)M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more aromatic rings; Y and Y′ are selected from O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation, wherein the term C₃₋₇ heterocyclyl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heterocyclic compounds which has from 3 to 7 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S, wherein the term C₅₋₁₀ heteroaryl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heteroaromatic compound which has from 5 to 10 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S.
 12. The Conjugate of claim 11, wherein

where the asterisk indicates the point of attachment to L¹, the wavy line indicates the point of attachment to the Ligand unit, and n is 0 to
 6. 13. The Conjugate of claim 11, wherein L¹ selected from an amino acid sequence, which is a dipeptide selected from the group consisting of valine-alanine, valine-citrulline and phenyalanine-lysine.
 14. A drug linker of formula V: LU-D  (V) or a pharmaceutically acceptable salt or solvate thereof, wherein LU is a Linker unit which is G¹-L¹, wherein G¹ is selected from:

where the asterisk indicates the point of attachment to L¹ and n is 0 to 6;

where the asterisk indicates the point of attachment to L¹ and n is 0 to 6;

where the asterisk indicates the point of attachment to L¹, n is 0 or 1, and m is 0 to 30;

where the asterisk indicates the point of attachment to L¹, n is 0 or 1, and m is 0 to 30; and wherein the above formulae the maleimide group may be replaced by —NH—C(O)—CH₂X, where X is Cl, Br or I, L¹ is selected from an amino acid sequence which is cleavable by the action of an enzyme and D is a Drug unit with the formula I:

wherein: R² is of formula II:

where A is phenyl, naphthyl or a C₅₋₇ heteroaryl group, X is selected from the group consisting of: *NHNH^(q), *CONHNH^(q),

where * indicates where the group is bound to the PBD moiety, and q indicates where the group is bound to the Linker Unit and either: Q¹ is a single bond, and Q² is selected from a single bond and —Z—(CH₂)_(n)—, where Z is selected from a single bond, O, S and NH and n is from 1 to 3; or (ii) Q¹ is —CH═CH—, and Q² is a single bond; R¹² is a phenyl, naphthyl, or C₅₋₁₀ heteroaryl group, optionally substituted by one or more substituents selected from the group consisting of: halo, nitro, cyano, C₁₋₇ alkoxy, C₁₋₇ alkyl, C₃₋₇ heterocyclyl and bis-oxy-C₁₋₃ alkylene; R⁶ and R⁹ are H; R⁷ is a C₁₋₄ alkoxy, optionally substituted by a C₅ heteroaryl or phenyl group; either: (a) R¹⁰ is H, and R¹¹ is OH, OR^(A), where R^(A) is C₁₋₄ alkyl; (b) R¹⁰ and R¹¹ form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound; or (c) R¹⁰ is H and R¹¹ is SO_(z)M, where z is 2 or 3 and M is a monovalent pharmaceutically acceptable cation; R″ is a C₃₋₁₂ alkylene group, which chain may be interrupted by one or more aromatic rings; Y and Y′ are selected from O, S, and NH; R^(6′), R^(7′), R^(9′) are selected from the same groups as R⁶, R⁷ and R⁹ respectively and R^(10′) and R^(11′) are the same as R¹⁰ and R¹¹, wherein if R¹¹ and R^(11′) are SO_(z)M, M may represent a divalent pharmaceutically acceptable cation, wherein the term C₃₋₇ heterocycyl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heterocyclic compounds which has from 3 to 7 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S, wherein the term C₅₋₁₀ heteroaryl refers to a monovalent moiety obtained by removing a hydrogen atom for a ring atom of a heteroaromatic compound which has from 5 to 10 ring atoms of which 1 to 4 are ring heteroatoms selected from N, O and S. 